Evidence is represented by a simple gml:dataSource or gml:dataSourceReference property that indicates the source of the temporal data. The remote link attributes of the gml:dataSource element have been deprecated along with its current type.
Element dataSourceReference
Evidence is represented by a simple gml:dataSource or gml:dataSourceReference property that indicates the source of the temporal data.
Element DynamicFeature
States are captured by time-stamped instances of a feature. The content model extends the standard gml:AbstractFeatureType with the gml:dynamicProperties model group.
Each time-stamped instance represents a 'snapshot' of a feature. The dynamic feature classes will normally be extended to suit particular applications. A dynamic feature bears either a time stamp or a history.
Element DynamicFeatureCollection
A gml:DynamicFeatureCollection is a feature collection that has a gml:validTime property (i.e. is a snapshot of the feature collection) or which has a gml:history property that contains one or more gml:AbstractTimeSlices each of which contain values of the time varying properties of the feature collection. Note that the gml:DynamicFeatureCollection may be one of the following:
1. A feature collection which consists of static feature members (members do not change in time) but which has properties of the collection object as a whole that do change in time .
2. A feature collection which consists of dynamic feature members (the members are gml:DynamicFeatures) but which also has properties of the collection as a whole that vary in time.
Element AbstractTimeSlice
To describe an event — an action that occurs at an instant or over an interval of time — GML provides the gml:AbtractTimeSlice element. A timeslice encapsulates the time-varying properties of a dynamic feature -- it shall be extended to represent a time stamped projection of a specific feature. The gml:dataSource property describes how the temporal data was acquired.
A gml:AbstractTimeSlice instance is a GML object that encapsulates updates of the dynamic—or volatile—properties that reflect some change event; it thus includes only those feature properties that have actually changed due to some process.
gml:AbstractTimeSlice basically provides a facility for attribute-level time stamping, in contrast to the object-level time stamping of dynamic feature instances.
The time slice can thus be viewed as event or process-oriented, whereas a snapshot is more state or structure-oriented. A timeslice has richer causality, whereas a snapshot merely portrays the status of the whole.
Element history
A generic sequence of events constitute a gml:history of an object.
The gml:history element contains a set of elements in the substitution group headed by the abstract element gml:AbstractTimeSlice, representing the time-varying properties of interest. The history property of a dynamic feature associates a feature instance with a sequence of time slices (i.e. change events) that encapsulate the evolution of the feature.
Element AbstractFeature
This abstract element serves as the head of a substitution group which may contain any elements whose content model is derived from gml:AbstractFeatureType. This may be used as a variable in the construction of content models.
gml:AbstractFeature may be thought of as "anything that is a GML feature" and may be used to define variables or templates in which the value of a GML property is "any feature". This occurs in particular in a GML feature collection where the feature member properties contain one or multiple copies of gml:AbstractFeature respectively.
Element boundedBy
This property describes the minimum bounding box or rectangle that encloses the entire feature.
Element EnvelopeWithTimePeriod
gml:EnvelopeWithTimePeriod is provided for envelopes that include a temporal extent. It adds two time position properties, gml:beginPosition and gml:endPosition, which describe the extent of a time-envelope.
Since gml:EnvelopeWithTimePeriod is assigned to the substitution group headed by gml:Envelope, it may be used whenever gml:Envelope is valid.
Element locationName
The gml:locationName property element is a convenience property where the text value describes the location of the feature. If the location names are selected from a controlled list, then the list shall be identified in the codeSpace attribute.
Element locationReference
The gml:locationReference property element is a convenience property where the text value referenced by the xlink:href attribute describes the location of the feature.
Element AbstractGeometricAggregate
gml:AbstractGeometricAggregate is the abstract head of the substitution group for all geometric aggregates.
Element MultiGeometry
gml:MultiGeometry is a collection of one or more GML geometry objects of arbitrary type.
The members of the geometric aggregate may be specified either using the "standard" property (gml:geometryMember) or the array property (gml:geometryMembers). It is also valid to use both the "standard" and the array properties in the same collection.
Element geometryMember
This property element either references a geometry element via the XLink-attributes or contains the geometry element.
Element geometryMembers
This property element contains a list of geometry elements. The order of the elements is significant and shall be preserved when processing the array.
Element MultiPoint
A gml:MultiPoint consists of one or more gml:Points.
The members of the geometric aggregate may be specified either using the "standard" property (gml:pointMember) or the array property (gml:pointMembers). It is also valid to use both the "standard" and the array properties in the same collection.
Element pointMember
This property element either references a Point via the XLink-attributes or contains the Point element.
Element pointMembers
This property element contains a list of points. The order of the elements is significant and shall be preserved when processing the array.
Element MultiCurve
A gml:MultiCurve is defined by one or more gml:AbstractCurves.
The members of the geometric aggregate may be specified either using the "standard" property (gml:curveMember) or the array property (gml:curveMembers). It is also valid to use both the "standard" and the array properties in the same collection.
Element curveMembers
This property element contains a list of curves. The order of the elements is significant and shall be preserved when processing the array.
Element MultiSurface
A gml:MultiSurface is defined by one or more gml:AbstractSurfaces.
The members of the geometric aggregate may be specified either using the "standard" property (gml:surfaceMember) or the array property (gml:surfaceMembers). It is also valid to use both the "standard" and the array properties in the same collection.
Element surfaceMembers
This property element contains a list of surfaces. The order of the elements is significant and shall be preserved when processing the array.
Element MultiSolid
A gml:MultiSolid is defined by one or more gml:AbstractSolids.
The members of the geometric aggregate may be specified either using the "standard" property (gml:solidMember) or the array property (gml:solidMembers). It is also valid to use both the "standard" and the array properties in the same collection.
Element solidMember
This property element either references a solid via the XLink-attributes or contains the solid element. A solid element is any element, which is substitutable for gml:AbstractSolid.
Element solidMembers
This property element contains a list of solids. The order of the elements is significant and shall be preserved when processing the array.
Element Curve
A curve is a 1-dimensional primitive. Curves are continuous, connected, and have a measurable length in terms of the coordinate system.
A curve is composed of one or more curve segments. Each curve segment within a curve may be defined using a different interpolation method. The curve segments are connected to one another, with the end point of each segment except the last being the start point of the next segment in the segment list.
The orientation of the curve is positive.
The element segments encapsulates the segments of the curve.
Element baseCurve
The property baseCurve references or contains the base curve, i.e. it either references the base curve via the XLink-attributes or contains the curve element. A curve element is any element which is substitutable for AbstractCurve. The base curve has positive orientation.
Element OrientableCurve
OrientableCurve consists of a curve and an orientation. If the orientation is "+", then the OrientableCurve is identical to the baseCurve. If the orientation is "-", then the OrientableCurve is related to another AbstractCurve with a parameterization that reverses the sense of the curve traversal.
Element AbstractCurveSegment
A curve segment defines a homogeneous segment of a curve.
The attributes numDerivativesAtStart, numDerivativesAtEnd and numDerivativesInterior specify the type of continuity as specified in ISO 19107:2003, 6.4.9.3.
The AbstractCurveSegment element is the abstract head of the substituition group for all curve segment elements, i.e. continuous segments of the same interpolation mechanism.
All curve segments shall have an attribute interpolation with type gml:CurveInterpolationType specifying the curve interpolation mechanism used for this segment. This mechanism uses the control points and control parameters to determine the position of this curve segment.
Element segments
This property element contains a list of curve segments. The order of the elements is significant and shall be preserved when processing the array.
Simple Type CurveInterpolationType
gml:CurveInterpolationType is a list of codes that may be used to identify the interpolation mechanisms specified by an application schema.
Element LineStringSegment
A LineStringSegment is a curve segment that is defined by two or more control points including the start and end point, with linear interpolation between them.
The content model follows the general pattern for the encoding of curve segments.
Element ArcString
An ArcString is a curve segment that uses three-point circular arc interpolation ("circularArc3Points"). The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be 2 * numArc + 1.
The content model follows the general pattern for the encoding of curve segments.
Element Arc
An Arc is an arc string with only one arc unit, i.e. three control points including the start and end point. As arc is an arc string consisting of a single arc, the attribute "numArc" is fixed to "1".
Element Circle
A Circle is an arc whose ends coincide to form a simple closed loop. The three control points shall be distinct non-co-linear points for the circle to be unambiguously defined. The arc is simply extended past the third control point until the first control point is encountered.
Element ArcStringByBulge
This variant of the arc computes the mid points of the arcs instead of storing the coordinates directly. The control point sequence consists of the start and end points of each arc plus the bulge (see ISO 19107:2003, 6.4.17.2). The normal is a vector normal (perpendicular) to the chord of the arc (see ISO 19107:2003, 6.4.17.4).
The interpolation is fixed as "circularArc2PointWithBulge".
The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be numArc + 1.
The content model follows the general pattern for the encoding of curve segments.
Element ArcByBulge
An ArcByBulge is an arc string with only one arc unit, i.e. two control points, one bulge and one normal vector.
As arc is an arc string consisting of a single arc, the attribute "numArc" is fixed to "1".
Element ArcByCenterPoint
This variant of the arc requires that the points on the arc shall be computed instead of storing the coordinates directly. The single control point is the center point of the arc plus the radius and the bearing at start and end. This representation can be used only in 2D.
The element radius specifies the radius of the arc.
The element startAngle specifies the bearing of the arc at the start.
The element endAngle specifies the bearing of the arc at the end.
The interpolation is fixed as "circularArcCenterPointWithRadius".
Since this type describes always a single arc, the attribute "numArc" is fixed to "1".
The content model follows the general pattern for the encoding of curve segments.
Element CircleByCenterPoint
A gml:CircleByCenterPoint is an gml:ArcByCenterPoint with identical start and end angle to form a full circle. Again, this representation can be used only in 2D.
Element CubicSpline
The number of control points shall be at least three.
vectorAtStart is the unit tangent vector at the start point of the spline. vectorAtEnd is the unit tangent vector at the end point of the spline. Only the direction of the vectors shall be used to determine the shape of the cubic spline, not their length.
interpolation is fixed as "cubicSpline".
degree shall be the degree of the polynomial used for the interpolation in this spline. Therefore the degree for a cubic spline is fixed to "3".
The content model follows the general pattern for the encoding of curve segments.
Element BSpline
A B-Spline is a piecewise parametric polynomial or rational curve described in terms of control points and basis functions as specified in ISO 19107:2003, 6.4.30. Therefore, interpolation may be either "polynomialSpline" or "rationalSpline" depending on the interpolation type; default is "polynomialSpline".
degree shall be the degree of the polynomial used for interpolation in this spline.
knot shall be the sequence of distinct knots used to define the spline basis functions (see ISO 19107:2003, 6.4.26.2).
The attribute isPolynomial shall be set to "true" if this is a polynomial spline (see ISO 19107:2003, 6.4.30.5).
The attribute knotType shall provide the type of knot distribution used in defining this spline (see ISO 19107:2003, 6.4.30.4).
The content model follows the general pattern for the encoding of curve segments.
Element Knot
A knot is a breakpoint on a piecewise spline curve.
value is the value of the parameter at the knot of the spline (see ISO 19107:2003, 6.4.24.2).
multiplicity is the multiplicity of this knot used in the definition of the spline (with the same weight).
weight is the value of the averaging weight used for this knot of the spline.
Simple Type KnotTypesType
This enumeration type specifies values for the knots' type (see ISO 19107:2003, 6.4.25).
Element Bezier
Bezier curves are polynomial splines that use Bezier or Bernstein polynomials for interpolation purposes. It is a special case of the B-Spline curve with two knots.
degree shall be the degree of the polynomial used for interpolation in this spline.
knot shall be the sequence of distinct knots used to define the spline basis functions.
interpolation is fixed as "polynomialSpline".
isPolynomial is fixed as "true".
knotType is not relevant for Bezier curve segments.
Element OffsetCurve
An offset curve is a curve at a constant distance from the basis curve. offsetBase is the base curve from which this curve is defined as an offset. distance and refDirection have the same meaning as specified in ISO 19107:2003, 6.4.23.
The content model follows the general pattern for the encoding of curve segments.
Element AffinePlacement
location, refDirection, inDimension and outDimension have the same meaning as specified in ISO 19107:2003, 6.4.21.
Element Clothoid
A clothoid, or Cornu's spiral, is plane curve whose curvature is a fixed function of its length.
refLocation, startParameter, endParameter and scaleFactor have the same meaning as specified in ISO 19107:2003, 6.4.22.
interpolation is fixed as "clothoid".
The content model follows the general pattern for the encoding of curve segments.
Element GeodesicString
A sequence of geodesic segments.
The number of control points shall be at least two.
interpolation is fixed as "geodesic".
The content model follows the general pattern for the encoding of curve segments.
Element Surface
A Surface is a 2-dimensional primitive and is composed of one or more surface patches as specified in ISO 19107:2003, 6.3.17.1. The surface patches are connected to one another.
patches encapsulates the patches of the surface.
Element baseSurface
The property baseSurface references or contains the base surface. The property baseSurface either references the base surface via the XLink-attributes or contains the surface element. A surface element is any element which is substitutable for gml:AbstractSurface. The base surface has positive orientation.
Element OrientableSurface
OrientableSurface consists of a surface and an orientation. If the orientation is "+", then the OrientableSurface is identical to the baseSurface. If the orientation is "-", then the OrientableSurface is a reference to a gml:AbstractSurface with an up-normal that reverses the direction for this OrientableSurface, the sense of "the top of the surface".
Element AbstractSurfacePatch
A surface patch defines a homogenuous portion of a surface.
The AbstractSurfacePatch element is the abstract head of the substituition group for all surface patch elements describing a continuous portion of a surface.
All surface patches shall have an attribute interpolation (declared in the types derived from gml:AbstractSurfacePatchType) specifying the interpolation mechanism used for the patch using gml:SurfaceInterpolationType.
Element patches
The patches property element contains the sequence of surface patches. The order of the elements is significant and shall be preserved when processing the array.
Simple Type SurfaceInterpolationType
gml:SurfaceInterpolationType is a list of codes that may be used to identify the interpolation mechanisms specified by an application schema.
Element PolygonPatch
A gml:PolygonPatch is a surface patch that is defined by a set of boundary curves and an underlying surface to which these curves adhere. The curves shall be coplanar and the polygon uses planar interpolation in its interior.
interpolation is fixed to "planar", i.e. an interpolation shall return points on a single plane. The boundary of the patch shall be contained within that plane.
Element Triangle
gml:Triangle represents a triangle as a surface patch with an outer boundary consisting of a linear ring. Note that this is a polygon (subtype) with no inner boundaries. The number of points in the linear ring shall be four.
The ring (element exterior) shall be a gml:LinearRing and shall form a triangle, the first and the last position shall be coincident.
interpolation is fixed to "planar", i.e. an interpolation shall return points on a single plane. The boundary of the patch shall be contained within that plane.
Element Rectangle
gml:Rectangle represents a rectangle as a surface patch with an outer boundary consisting of a linear ring. Note that this is a polygon (subtype) with no inner boundaries. The number of points in the linear ring shall be five.
The ring (element exterior) shall be a gml:LinearRing and shall form a rectangle; the first and the last position shall be coincident.
interpolation is fixed to "planar", i.e. an interpolation shall return points on a single plane. The boundary of the patch shall be contained within that plane.
Element Ring
A ring is used to represent a single connected component of a surface boundary as specified in ISO 19107:2003, 6.3.6.
Every gml:curveMember references or contains one curve, i.e. any element which is substitutable for gml:AbstractCurve. In the context of a ring, the curves describe the boundary of the surface. The sequence of curves shall be contiguous and connected in a cycle.
If provided, the aggregationType attribute shall have the value "sequence".
Element AbstractParametricCurveSurface
The element provides a substitution group head for the surface patches based on parametric curves. All properties are specified in the derived subtypes. All derived subtypes shall conform to the constraints specified in ISO 19107:2003, 6.4.40.
If provided, the aggregationType attribute shall have the value "set".
Element AbstractGriddedSurface
if provided, rows gives the number of rows, columns the number of columns in the parameter grid. The parameter grid is represented by an instance of the gml:PointGrid group.
The element provides a substitution group head for the surface patches based on a grid. All derived subtypes shall conform to the constraints specified in ISO 19107:2003, 6.4.41.
Element PolyhedralSurface
A polyhedral surface is a surface composed of polygon patches connected along their common boundary curves. This differs from the surface type only in the restriction on the types of surface patches acceptable.
polygonPatches encapsulates the polygon patches of the polyhedral surface.
Element TriangulatedSurface
A triangulated surface is a polyhedral surface that is composed only of triangles. There is no restriction on how the triangulation is derived.
trianglePatches encapsulates the triangles of the triangulated surface.
Element Tin
A tin is a triangulated surface that uses the Delauny algorithm or a similar algorithm complemented with consideration of stoplines (stopLines), breaklines (breakLines), and maximum length of triangle sides (maxLength). controlPoint shall contain a set of the positions (three or more) used as posts for this TIN (corners of the triangles in the TIN). See ISO 19107:2003, 6.4.39 for details.
Element AbstractSolid
The AbstractSolid element is the abstract head of the substituition group for all (continuous) solid elements.
Element solidProperty
This property element either references a solid via the XLink-attributes or contains the solid element. solidProperty is the predefined property which may be used by GML Application Schemas whenever a GML feature has a property with a value that is substitutable for AbstractSolid.
Element Solid
A solid is the basis for 3-dimensional geometry. The extent of a solid is defined by the boundary surfaces as specified in ISO 19107:2003, 6.3.18. exterior specifies the outer boundary, interior the inner boundary of the solid.
Element Shell
A shell is used to represent a single connected component of a solid boundary as specified in ISO 19107:2003, 6.3.8.
Every gml:surfaceMember references or contains one surface, i.e. any element which is substitutable for gml:AbstractSurface. In the context of a shell, the surfaces describe the boundary of the solid.
If provided, the aggregationType attribute shall have the value "set".
Element surfaceMember
This property element either references a surface via the XLink-attributes or contains the surface element. A surface element is any element, which is substitutable for gml:AbstractSurface.
Element AbstractSurface
The AbstractSurface element is the abstract head of the substitution group for all (continuous) surface elements.
Element surfaceProperty
This property element either references a surface via the XLink-attributes or contains the surface element. surfaceProperty is the predefined property which may be used by GML Application Schemas whenever a GML feature has a property with a value that is substitutable for AbstractSurface.
Element Polygon
A Polygon is a special surface that is defined by a single surface patch (see D.3.6). The boundary of this patch is coplanar and the polygon uses planar interpolation in its interior.
The elements exterior and interior describe the surface boundary of the polygon.
Element exterior
A boundary of a surface consists of a number of rings. In the normal 2D case, one of these rings is distinguished as being the exterior boundary. In a general manifold this is not always possible, in which case all boundaries shall be listed as interior boundaries, and the exterior will be empty.
Element interior
A boundary of a surface consists of a number of rings. The "interior" rings separate the surface / surface patch from the area enclosed by the rings.
Element AbstractRing
An abstraction of a ring to support surface boundaries of different complexity.
The AbstractRing element is the abstract head of the substituition group for all closed boundaries of a surface patch.
Element LinearRing
A LinearRing is defined by four or more coordinate tuples, with linear interpolation between them; the first and last coordinates shall be coincident. The number of direct positions in the list shall be at least four.
Element AbstractGeometry
The AbstractGeometry element is the abstract head of the substitution group for all geometry elements of GML. This includes pre-defined and user-defined geometry elements. Any geometry element shall be a direct or indirect extension/restriction of AbstractGeometryType and shall be directly or indirectly in the substitution group of AbstractGeometry.
Element Envelope
Envelope defines an extent using a pair of positions defining opposite corners in arbitrary dimensions. The first direct position is the "lower corner" (a coordinate position consisting of all the minimal ordinates for each dimension for all points within the envelope), the second one the "upper corner" (a coordinate position consisting of all the maximal ordinates for each dimension for all points within the envelope).
The use of the properties "coordinates" and "pos" has been deprecated. The explicitly named properties "lowerCorner" and "upperCorner" shall be used instead.
Element AbstractGeometricPrimitive
The AbstractGeometricPrimitive element is the abstract head of the substitution group for all (pre- and user-defined) geometric primitives.
Element Point
A Point is defined by a single coordinate tuple. The direct position of a point is specified by the pos element which is of type DirectPositionType.
Element pointProperty
This property element either references a point via the XLink-attributes or contains the point element. pointProperty is the predefined property which may be used by GML Application Schemas whenever a GML feature has a property with a value that is substitutable for Point.
Element AbstractCurve
The AbstractCurve element is the abstract head of the substitution group for all (continuous) curve elements.
Element curveProperty
This property element either references a curve via the XLink-attributes or contains the curve element. curveProperty is the predefined property which may be used by GML Application Schemas whenever a GML feature has a property with a value that is substitutable for AbstractCurve.
Element LineString
A LineString is a special curve that consists of a single segment with linear interpolation. It is defined by two or more coordinate tuples, with linear interpolation between them. The number of direct positions in the list shall be at least two.
Element measure
The value of a physical quantity, together with its unit.
Element angle
The gml:angle property element is used to record the value of an angle quantity as a single number, with its units.
Element unitOfMeasure
The element gml:unitOfMeasure is a property element to refer to a unit of measure. This is an empty element which carries a reference to a unit of measure definition.
Element UnitDefinition
A gml:UnitDefinition is a general definition of a unit of measure. This generic element is used only for units for which no relationship with other units or units systems is known.
The content model of gml:UnitDefinition adds three additional properties to gml:Definition, gml:quantityType, gml:quantityTypeReference and gml:catalogSymbol.
The gml:catalogSymbol property optionally gives the short symbol used for this unit. This element is usually used when the relationship of this unit to other units or units systems is unknown.
Element quantityType
The gml:quantityType property indicates the phenomenon to which the units apply. This element contains an informal description of the phenomenon or type of physical quantity that is measured or observed. When the physical quantity is the result of an observation or measurement, this term is known as observable type or measurand.
The use of gml:quantityType for references to remote values is deprecated.
Element quantityTypeReference
The gml:quantityTypeReference property indicates the phenomenon to which the units apply. The content is a reference to a remote value.
Element catalogSymbol
The catalogSymbol is the preferred lexical symbol used for this unit of measure.
The codeSpace attribute in gml:CodeType identifies a namespace for the catalog symbol value, and might reference the external catalog. The string value in gml:CodeType contains the value of a symbol that should be unique within this catalog namespace. This symbol often appears explicitly in the catalog, but it could be a combination of symbols using a specified algebra of units.
Element BaseUnit
A base unit is a unit of measure that cannot be derived by combination of other base units within a particular system of units. For example, in the SI system of units, the base units are metre, kilogram, second, Ampere, Kelvin, mole, and candela, for the physical quantity types length, mass, time interval, electric current, thermodynamic temperature, amount of substance and luminous intensity, respectively.
gml:BaseUnit extends generic gml:UnitDefinition with the property gml:unitsSystem, which carries a reference to the units system to which this base unit is asserted to belong.
Element DerivedUnit
Derived units are defined by combination of other units. Derived units are used for quantities other than those corresponding to the base units, such as hertz (s-1) for frequency, Newton (kg.m/s2) for force. Derived units based directly on base units are usually preferred for quantities other than the fundamental quantities within a system. If a derived unit is not the preferred unit, the gml:ConventionalUnit element should be used instead.
The gml:DerivedUnit extends gml:UnitDefinition with the property gml:derivationUnitTerms.
Element derivationUnitTerm
A set of gml:derivationUnitTerm elements describes a derived unit of measure. Each element carries an integer exponent. The terms are combined by raising each referenced unit to the power of its exponent and forming the product.
This unit term references another unit of measure (uom) and provides an integer exponent applied to that unit in defining the compound unit. The exponent may be positive or negative, but not zero.
Element ConventionalUnit
Conventional units that are neither base units nor defined by direct combination of base units are used in many application domains. For example electronVolt for energy, feet and nautical miles for length. In most cases there is a known, usually linear, conversion to a preferred unit which is either a base unit or derived by direct combination of base units.
The gml:ConventionalUnit extends gml:UnitDefinition with a property that describes a conversion to a preferred unit for this physical quantity. When the conversion is exact, the element gml:conversionToPreferredUnit should be used, or when the conversion is not exact the element gml:roughConversionToPreferredUnit is available. Both of these elements have the same content model. The gml:derivationUnitTerm property defined above is included to allow a user to optionally record how this unit may be derived from other ("more primitive") units.
Element conversionToPreferredUnit
The elements gml:conversionToPreferredUnit and gml:roughConversionToPreferredUnit represent parameters used to convert conventional units to preferred units for this physical quantity type. A preferred unit is either a Base Unit or a Derived Unit that is selected for all values of one physical quantity type.
Element roughConversionToPreferredUnit
The elements gml:conversionToPreferredUnit and gml:roughConversionToPreferredUnit represent parameters used to convert conventional units to preferred units for this physical quantity type. A preferred unit is either a Base Unit or a Derived Unit that is selected for all values of one physical quantity type.
Element Definition
The basic gml:Definition element specifies a definition, which can be included in or referenced by a dictionary.
The content model for a generic definition is a derivation from gml:AbstractGMLType.
The gml:description property element shall hold the definition if this can be captured in a simple text string, or the gml:descriptionReference property element may carry a link to a description elsewhere.
The gml:identifier element shall provide one identifier identifying this definition. The identifier shall be unique within the dictionaries using this definition.
The gml:name elements shall provide zero or more terms and synonyms for which this is the definition.
The gml:remarks element shall be used to hold additional textual information that is not conceptually part of the definition but is useful in understanding the definition.
Element Dictionary
Sets of definitions may be collected into dictionaries or collections.
A gml:Dictionary is a non-abstract collection of definitions.
The gml:Dictionary content model adds a list of gml:dictionaryEntry properties that contain or reference gml:Definition objects. A database handle (gml:id attribute) is required, in order that this collection may be referred to. The standard gml:identifier, gml:description, gml:descriptionReference and gml:name properties are available to reference or contain more information about this dictionary. The gml:description and gml:descriptionReference property elements may be used for a description of this dictionary. The derived gml:name element may be used for the name(s) of this dictionary. for remote definiton references gml:dictionaryEntry shall be used. If a Definition object contained within a Dictionary uses the descriptionReference property to refer to a remote definition, then this enables the inclusion of a remote definition in a local dictionary, giving a handle and identifier in the context of the local dictionary.
Element dictionaryEntry
This property element contains or refers to the definitions which are members of a dictionary.
The content model follows the standard GML property pattern, so a gml:dictionaryEntry may either contain or refer to a single gml:Definition. Since gml:Dictionary is substitutable for gml:Definition, the content of an entry may itself be a lower level dictionary.
Note that if the value is provided by reference, this definition does not carry a handle (gml:id) in this context, so does not allow external references to this specific definition in this context. When used in this way the referenced definition will usually be in a dictionary in the same XML document.
Element AbstractObject
This element has no type defined, and is therefore implicitly (according to the rules of W3C XML Schema) an XML Schema anyType. It is used as the head of an XML Schema substitution group which unifies complex content and certain simple content elements used for datatypes in GML, including the gml:AbstractGML substitution group.
Element AbstractGML
The abstract element gml:AbstractGML is "any GML object having identity". It acts as the head of an XML Schema substitution group, which may include any element which is a GML feature, or other object, with identity. This is used as a variable in content models in GML core and application schemas. It is effectively an abstract superclass for all GML objects.
Element abstractAssociationRole
Applying this pattern shall restrict the multiplicity of objects in a property element using this content model to exactly one. An instance of this type shall contain an element representing an object, or serve as a pointer to a remote object.
Applying the pattern to define an application schema specific property type allows to restrict
- the inline object to specified object types,
- the encoding to "by-reference only" (see 7.2.3.7),
- the encoding to "inline only" (see 7.2.3.8).
Element abstractStrictAssociationRole
This element shows how an element
declaration may include a Schematron constraint to limit the property to act
in either inline or by-reference mode, but not both.
Element abstractReference
gml:abstractReference may be used as the head of a subtitution group of more specific elements providing a value by-reference.
Element abstractInlineProperty
gml:abstractInlineProperty may be used as the head of a subtitution group of more specific elements providing a value inline.
Element reversePropertyName
If the value of an object property is another object and that object contains also a property for the association between the two objects, then this name of the reverse property may be encoded in a gml:reversePropertyName element in an appinfo annotation of the property element to document the constraint between the two properties. The value of the element shall contain the qualified name of the property element.
Element description
The value of this property is a text description of the object. gml:description uses gml:StringOrRefType as its content model, so it may contain a simple text string content, or carry a reference to an external description. The use of gml:description to reference an external description has been deprecated and replaced by the gml:descriptionReference property.
Element descriptionReference
The value of this property is a remote text description of the object. The xlink:href attribute of the gml:descriptionReference property references the external description.
Element name
The gml:name property provides a label or identifier for the object, commonly a descriptive name. An object may have several names, typically assigned by different authorities. gml:name uses the gml:CodeType content model. The authority for a name is indicated by the value of its (optional) codeSpace attribute. The name may or may not be unique, as determined by the rules of the organization responsible for the codeSpace. In common usage there will be one name per authority, so a processing application may select the name from its preferred codeSpace.
Element identifier
Often, a special identifier is assigned to an object by the maintaining authority with the intention that it is used in references to the object For such cases, the codeSpace shall be provided. That identifier is usually unique either globally or within an application domain. gml:identifier is a pre-defined property for such identifiers.
Attribute id
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
Simple Type NilReasonType
gml:NilReasonType defines a content model that allows recording of an explanation for a void value or other exception.
gml:NilReasonType is a union of the following enumerated values:
- inapplicable there is no value
- missing the correct value is not readily available to the sender of this data. Furthermore, a correct value may not exist
- template the value will be available later
- unknown the correct value is not known to, and not computable by, the sender of this data. However, a correct value probably exists
- withheld the value is not divulged
- other:text other brief explanation, where text is a string of two or more characters with no included spaces
and
- anyURI which should refer to a resource which describes the reason for the exception
A particular community may choose to assign more detailed semantics to the standard values provided. Alternatively, the URI method enables a specific or more complete explanation for the absence of a value to be provided elsewhere and indicated by-reference in an instance document.
gml:NilReasonType is used as a member of a union in a number of simple content types where it is necessary to permit a value from the NilReasonType union as an alternative to the primary type.
Simple Type SignType
gml:SignType is a convenience type with values "+" (plus) and "-" (minus).
Simple Type booleanOrNilReason
Extension to the respective XML Schema built-in simple type to allow a choice of either a value of the built-in simple type or a reason for a nil value.
Simple Type doubleOrNilReason
Extension to the respective XML Schema built-in simple type to allow a choice of either a value of the built-in simple type or a reason for a nil value.
Simple Type integerOrNilReason
Extension to the respective XML Schema built-in simple type to allow a choice of either a value of the built-in simple type or a reason for a nil value.
Simple Type NameOrNilReason
Extension to the respective XML Schema built-in simple type to allow a choice of either a value of the built-in simple type or a reason for a nil value.
Simple Type stringOrNilReason
Extension to the respective XML Schema built-in simple type to allow a choice of either a value of the built-in simple type or a reason for a nil value.
Simple Type UomIdentifier
The simple type gml:UomIdentifer defines the syntax and value space of the unit of measure identifier.
Simple Type UomSymbol
This type specifies a character string of length at least one, and restricted such that it must not contain any of the following characters: ":" (colon), " " (space), (newline), (carriage return), (tab). This allows values corresponding to familiar abbreviations, such as "kg", "m/s", etc.
It is recommended that the symbol be an identifier for a unit of measure as specified in the "Unified Code of Units of Measure" (UCUM) (http://aurora.regenstrief.org/UCUM). This provides a set of symbols and a grammar for constructing identifiers for units of measure that are unique, and may be easily entered with a keyboard supporting the limited character set known as 7-bit ASCII. ISO 2955 formerly provided a specification with this scope, but was withdrawn in 2001. UCUM largely follows ISO 2955 with modifications to remove ambiguities and other problems.
Simple Type UomURI
This type specifies a URI, restricted such that it must start with one of the following sequences: "#", "./", "../", or a string of characters followed by a ":". These patterns ensure that the most common URI forms are supported, including absolute and relative URIs and URIs that are simple fragment identifiers, but prohibits certain forms of relative URI that could be mistaken for unit of measure symbol .
NOTE It is possible to re-write such a relative URI to conform to the restriction (e.g. "./m/s").
In an instance document, on elements of type gml:MeasureType the mandatory uom attribute shall carry a value corresponding to either
- a conventional unit of measure symbol,
- a link to a definition of a unit of measure that does not have a conventional symbol, or when it is desired to indicate a precise or variant definition.
Simple Type booleanList
A type for a list of values of the respective simple type.
Simple Type doubleList
A type for a list of values of the respective simple type.
Simple Type integerList
A type for a list of values of the respective simple type.
Simple Type NameList
A type for a list of values of the respective simple type.
Simple Type NCNameList
A type for a list of values of the respective simple type.
Simple Type QNameList
A type for a list of values of the respective simple type.
Simple Type booleanOrNilReasonList
A type for a list of values of the respective simple type.
Simple Type NameOrNilReasonList
A type for a list of values of the respective simple type.
Simple Type doubleOrNilReasonList
A type for a list of values of the respective simple type.
Simple Type integerOrNilReasonList
A type for a list of values of the respective simple type.
Element AbstractTimeObject
gml:AbstractTimeObject acts as the head of a substitution group for all temporal primitives and complexes.
Element AbstractTimePrimitive
gml:AbstractTimePrimitive acts as the head of a substitution group for geometric and topological temporal primitives.
Element validTime
gml:validTime is a convenience property element.
Element AbstractTimeComplex
gml:AbstractTimeComplex is an aggregation of temporal primitives and acts as the head of a substitution group for temporal complexes.
Element AbstractTimeGeometricPrimitive
gml:TimeGeometricPrimitive acts as the head of a substitution group for geometric temporal primitives.
A temporal geometry shall be associated with a temporal reference system through the frame attribute that provides a URI reference that identifies a description of the reference system. Following ISO 19108, the Gregorian calendar with UTC is the default reference system, but others may also be used. The GPS calendar is an alternative reference systems in common use.
The two geometric primitives in the temporal dimension are the instant and the period. GML components are defined to support these as follows.
Element TimeInstant
gml:TimeInstant acts as a zero-dimensional geometric primitive that represents an identifiable position in time.
Element TimePeriod
gml:TimePeriod acts as a one-dimensional geometric primitive that represents an identifiable extent in time.
The location in of a gml:TimePeriod is described by the temporal positions of the instants at which it begins and ends. The length of the period is equal to the temporal distance between the two bounding temporal positions.
Both beginning and end may be described in terms of their direct position using gml:TimePositionType which is an XML Schema simple content type, or by reference to an indentifiable time instant using gml:TimeInstantPropertyType.
Alternatively a limit of a gml:TimePeriod may use the conventional GML property model to make a reference to a time instant described elsewhere, or a limit may be indicated as a direct position.
Simple Type TimeIndeterminateValueType
These values are interpreted as follows:
- "unknown" indicates that no specific value for temporal position is provided.
- "now" indicates that the specified value shall be replaced with the current temporal position whenever the value is accessed.
- "before" indicates that the actual temporal position is unknown, but it is known to be before the specified value.
- "after" indicates that the actual temporal position is unknown, but it is known to be after the specified value.
A value for indeterminatePosition may
- be used either alone, or
- qualify a specific value for temporal position.
Simple Type TimePositionUnion
The simple type gml:TimePositionUnion is a union of XML Schema simple types which instantiate the subtypes for temporal position described in ISO 19108.
An ordinal era may be referenced via URI. A decimal value may be used to indicate the distance from the scale origin . time is used for a position that recurs daily (see ISO 19108:2002 5.4.4.2).
Finally, calendar and clock forms that support the representation of time in systems based on years, months, days, hours, minutes and seconds, in a notation following ISO 8601, are assembled by gml:CalDate
Element timePosition
This element is used directly as a property of gml:TimeInstant (see 15.2.2.3), and may also be used in application schemas.
Element duration
gml:duration conforms to the ISO 8601 syntax for temporal length as implemented by the XML Schema duration type.
Element timeInterval
gml:timeInterval conforms to ISO 11404 which is based on floating point values for temporal length.
ISO 11404 syntax specifies the use of a positiveInteger together with appropriate values for radix and factor. The resolution of the time interval is to one radix ^(-factor) of the specified time unit.
The value of the unit is either selected from the units for time intervals from ISO 31-1:1992, or is another suitable unit. The encoding is defined for GML in gml:TimeUnitType. The second component of this union type provides a method for indicating time units other than the six standard units given in the enumeration.
Element direction
The property gml:direction is intended as a pre-defined property expressing a direction to be assigned to features defined in a GML application schema.
Simple Type CompassPointEnumeration
These directions are necessarily approximate, giving direction with a precision of 22.5°. It is thus generally unnecessary to specify the reference frame, though this may be detailed in the definition of a GML application language.
Element AbstractTopoPrimitive
gml:AbstractTopoPrimitive acts as the base type for all topological primitives. Topology primitives are the atomic (smallest possible) units of a topology complex.
Each topology primitive may contain references to other topology primitives of codimension 2 or more (gml:isolated). Conversely, nodes may have faces as containers and nodes and edges may have solids as containers (gml:container).
Element directedEdge
In the case of planar topology, a gml:Node must have a clockwise sequence of gml:directedEdge properties, to ensure a lossless topology representation as defined by Kuijpers, et. al. (see OGC 05-102 Topology IPR).
Element Node
gml:Node represents the 0-dimensional primitive.
The optional coboundary of a node (gml:directedEdge) is a sequence of directed edges which are incident on this node. Edges emanating from this node appear in the node coboundary with a negative orientation.
If provided, the aggregationType attribute shall have the value "sequence".
A node may optionally be realised by a 0-dimensional geometric primitive (gml:pointProperty).
Element directedNode
A gml:directedNode property element describes the boundary of topology edges and is used in the support of topological point features via the gml:TopoPoint expression, see below. The orientation attribute of type gml:SignType expresses the sense in which the included node is used: start ("-") or end ("+") node.
Element Edge
gml:Edge represents the 1-dimensional primitive.
The topological boundary of an Edge (gml:directedNode) consists of a negatively directed start Node and a positively directed end Node.
The optional coboundary of an edge (gml:directedFace) is a circular sequence of directed faces which are incident on this edge in document order. In the 2D case, the orientation of the face on the left of the edge is "+"; the orientation of the face on the right on its right is "-".
If provided, the aggregationType attribute shall have the value "sequence".
An edge may optionally be realised by a 1-dimensional geometric primitive (gml:curveProperty).
Element directedEdge
A gml:directedEdge property element describes the boundary of topology faces, the coBoundary of topology nodes and is used in the support of topological line features via the gml:TopoCurve expression, see below. The orientation attribute of type gml:SignType expresses the sense in which the included edge is used, i.e. forward or reverse.
Attribute universal
If the topological representation exists an unbounded manifold (e.g. Euclidean plane), a gml:Face must indicate whether it is a universal face or not, to ensure a lossless topology representation as defined by Kuijpers, et. al. (see OGC 05-102 Topology IPR). The optional universal attribute of type boolean is used to indicate this. NOTE The universal face is normally not part of any feature, and is used to represent the unbounded portion of the data set. Its interior boundary (it has no exterior boundary) would normally be considered the exterior boundary of the map represented by the data set.
Element Face
gml:Face represents the 2-dimensional topology primitive.
The topological boundary of a face (gml:directedEdge) consists of a sequence of directed edges. If provided, the aggregationType attribute shall have the value "sequence".
The optional coboundary of a face (gml:directedTopoSolid) is a pair of directed solids which are bounded by this face. A positively directed solid corresponds to a solid which lies in the direction of the negatively directed normal to the face in any geometric realisation.
A face may optionally be realised by a 2-dimensional geometric primitive (gml:surfaceProperty).
Element directedFace
The gml:directedFace property element describes the boundary of topology solids, in the coBoundary of topology edges and is used in the support of surface features via the gml:TopoSurface expression, see below. The orientation attribute of type gml:SignType expresses the sense in which the included face is used i.e. inward or outward with respect to the surface normal in any geometric realisation.
Attribute universal
A gml:TopoSolid must indicate whether it is a universal topo-solid or not, to ensure a lossless topology representation as defined by Kuijpers, et. al. (see OGC 05-102 Topology IPR). The optional universal attribute of type boolean is used to indicate this and the default is fault. NOTE The universal topo-solid is normally not part of any feature, and is used to represent the unbounded portion of the data set. Its interior boundary (it has no exterior boundary) would normally be considered the exterior boundary of the data set.
Element TopoSolid
gml:TopoSolid represents the 3-dimensional topology primitive.
The topological boundary of a solid (gml:directedFace) consists of a set of directed faces.
A solid may optionally be realised by a 3-dimensional geometric primitive (gml:solidProperty).
Element directedTopoSolid
The gml:directedSolid property element describes the coBoundary of topology faces and is used in the support of volume features via the gml:TopoVolume expression, see below. The orientation attribute of type gml:SignType expresses the sense in which the included solid appears in the face coboundary. In the context of a gml:TopoVolume the orientation attribute has no meaning.
Element TopoPoint
The intended use of gml:TopoPoint is to appear within a point feature to express the structural and possibly geometric relationships of this feature to other features via shared node definitions.
Element topoPointProperty
The gml:topoPointProperty property element may be used in features to express their relationship to the referenced topology node.
Element TopoCurve
gml:TopoCurve represents a homogeneous topological expression, a sequence of directed edges, which if realised are isomorphic to a geometric curve primitive. The intended use of gml:TopoCurve is to appear within a line feature to express the structural and geometric relationships of this feature to other features via the shared edge definitions.
If provided, the aggregationType attribute shall have the value "sequence".
Element topoCurveProperty
The gml:topoCurveProperty property element may be used in features to express their relationship to the referenced topology edges.
Element TopoSurface
gml:TopoSurface represents a homogeneous topological expression, a set of directed faces, which if realised are isomorphic to a geometric surface primitive. The intended use of gml:TopoSurface is to appear within a surface feature to express the structural and possibly geometric relationships of this surface feature to other features via the shared face definitions.
Element topoSurfaceProperty
The gml:topoSurfaceProperty property element may be used in features to express their relationship to the referenced topology faces.
Element TopoVolume
gml:TopoVolume represents a homogeneous topological expression, a set of directed topologic solids, which if realised are isomorphic to a geometric solid primitive. The intended use of gml:TopoVolume is to appear within a solid feature to express the structural and geometric relationships of this solid feature to other features via the shared solid definitions.
Element topoVolumeProperty
The gml:topoVolumeProperty element may be used in features to express their relationship to the referenced topology volume.
Element TopoComplex
gml:TopoComplex is a collection of topological primitives.
Each complex holds a reference to its maximal complex (gml:maximalComplex) and optionally to sub- or super-complexes (gml:subComplex, gml:superComplex).
A topology complex contains its primitive and sub-complex members.
Element subComplex
The property elements gml:subComplex, gml:superComplex and gml:maximalComplex provide an encoding for relationships between topology complexes as described for gml:TopoComplex above.
Element superComplex
The property elements gml:subComplex, gml:superComplex and gml:maximalComplex provide an encoding for relationships between topology complexes as described for gml:TopoComplex above.
Element maximalComplex
The property elements gml:subComplex, gml:superComplex and gml:maximalComplex provide an encoding for relationships between topology complexes as described for gml:TopoComplex above.
Element topoPrimitiveMember
The gml:topoPrimitiveMember property element encodes for the relationship between a topology complex and a single topology primitive.
Element topoPrimitiveMembers
The gml:topoPrimitiveMembers property element encodes the relationship between a topology complex and an arbitrary number of topology primitives.
Element CompositeCurve
A gml:CompositeCurve is represented by a sequence of (orientable) curves such that each curve in the sequence terminates at the start point of the subsequent curve in the list.
curveMember references or contains inline one curve in the composite curve.
The curves are contiguous, the collection of curves is ordered. Therefore, if provided, the aggregationType attribute shall have the value "sequence".
Element CompositeSurface
A gml:CompositeSurface is represented by a set of orientable surfaces. It is geometry type with all the geometric properties of a (primitive) surface. Essentially, a composite surface is a collection of surfaces that join in pairs on common boundary curves and which, when considered as a whole, form a single surface.
surfaceMember references or contains inline one surface in the composite surface.
The surfaces are contiguous.
Element CompositeSolid
gml:CompositeSolid implements ISO 19107 GM_CompositeSolid (see ISO 19107:2003, 6.6.7) as specified in D.2.3.6.
A gml:CompositeSolid is represented by a set of orientable surfaces. It is a geometry type with all the geometric properties of a (primitive) solid. Essentially, a composite solid is a collection of solids that join in pairs on common boundary surfaces and which, when considered as a whole, form a single solid.
solidMember references or contains one solid in the composite solid. The solids are contiguous.
Element AbstractCoverage
This element serves as the head of a substitution group which may contain any coverage whose type is derived from gml:AbstractCoverageType. It may act as a variable in the definition of content models where it is required to permit any coverage to be valid.
Element AbstractDiscreteCoverage
A discrete coverage consists of a domain set, range set and optionally a coverage function. The domain set consists of either spatial or temporal geometry objects, finite in number. The range set is comprised of a finite number of attribute values each of which is associated to every direct position within any single spatiotemporal object in the domain. In other words, the range values are constant on each spatiotemporal object in the domain. This coverage function maps each element from the coverage domain to an element in its range. The coverageFunction element describes the mapping function.
This element serves as the head of a substitution group which may contain any discrete coverage whose type is derived from gml:DiscreteCoverageType.
Element AbstractContinuousCoverage
A continuous coverage as defined in ISO 19123 is a coverage that can return different values for the same feature attribute at different direct positions within a single spatiotemporal object in its spatiotemporal domain. The base type for continuous coverages is AbstractContinuousCoverageType.
The coverageFunction element describes the mapping function.
The abstract element gml:AbstractContinuousCoverage serves as the head of a substitution group which may contain any continuous coverage whose type is derived from gml:AbstractContinuousCoverageType.
Element domainSet
The gml:domainSet property element describes the spatio-temporal region of interest, within which the coverage is defined. Its content model is given by gml:DomainSetType.
The value of the domain is thus a choice between a gml:AbstractGeometry and a gml:AbstractTimeObject. In the instance these abstract elements will normally be substituted by a geometry complex or temporal complex, to represent spatial coverages and time-series, respectively.
The presence of the gml:AssociationAttributeGroup means that domainSet follows the usual GML property model and may use the xlink:href attribute to point to the domain, as an alternative to describing the domain inline. Ownership semantics may be provided using the gml:OwnershipAttributeGroup.
Element rangeSet
The gml:rangeSet property element contains the values of the coverage (sometimes called the attribute values). Its content model is given by gml:RangeSetType.
This content model supports a structural description of the range. The semantic information describing the range set is embedded using a uniform method, as part of the explicit values, or as a template value accompanying the representation using gml:DataBlock and gml:File.
The values from each component (or "band") in the range may be encoded within a gml:ValueArray element or a concrete member of the gml:AbstractScalarValueList substitution group . Use of these elements satisfies the value-type homogeneity requirement.
Element DataBlock
gml:DataBlock describes the Range as a block of text encoded values similar to a Common Separated Value (CSV) representation.
The range set parameterization is described by the property gml:rangeParameters.
Element tupleList
gml:CoordinatesType consists of a list of coordinate tuples, with each coordinate tuple separated by the ts or tuple separator (whitespace), and each coordinate in the tuple by the cs or coordinate separator (comma).
The gml:tupleList encoding is effectively "band-interleaved".
Element doubleOrNilReasonTupleList
gml:doubleOrNilReasonList consists of a list of gml:doubleOrNilReason values, each separated by a whitespace. The gml:doubleOrNilReason values are grouped into tuples where the dimension of each tuple in the list is equal to the number of range parameters.
Element File
for efficiency reasons, GML also provides a means of encoding the range set in an arbitrary external encoding, such as a binary file. This encoding may be "well-known" but this is not required. This mode uses the gml:File element.
The values of the coverage (attribute values in the range set) are transmitted in a external file that is referenced from the XML structure described by gml:FileType. The external file is referenced by the gml:fileReference property that is an anyURI (the gml:fileName property has been deprecated). This means that the external file may be located remotely from the referencing GML instance.
The gml:compression property points to a definition of a compression algorithm through an anyURI. This may be a retrievable, computable definition or simply a reference to an unambiguous name for the compression method.
The gml:mimeType property points to a definition of the file mime type.
The gml:fileStructure property is defined by a codelist. Note further that all values shall be enclosed in a single file. Multi-file structures for values are not supported in GML.
The semantics of the range set is described as above using the gml:rangeParameters property.
Note that if any compression algorithm is applied, the structure above applies only to the pre-compression or post-decompression structure of the file.
Note that the fields within a record match the gml:valueComponents of the gml:CompositeValue in document order.
Element coverageFunction
The gml:coverageFunction property describes the mapping function from the domain to the range of the coverage.
The value of the CoverageFunction is one of gml:CoverageMappingRule and gml:GridFunction.
If the gml:coverageFunction property is omitted for a gridded coverage (including rectified gridded coverages) the gml:startPoint is assumed to be the value of the gml:low property in the gml:Grid geometry, and the gml:sequenceRule is assumed to be linear and the gml:axisOrder property is assumed to be "+1 +2".
Element CoverageMappingRule
gml:CoverageMappingRule provides a formal or informal description of the coverage function.
The mapping rule may be defined as an in-line string (gml:ruleDefinition) or via a remote reference through xlink:href (gml:ruleReference).
If no rule name is specified, the default is 'Linear' with respect to members of the domain in document order.
Element GridFunction
gml:GridFunction provides an explicit mapping rule for grid geometries, i.e. the domain shall be a geometry of type grid. It describes the mapping of grid posts (discrete point grid coverage) or grid cells (discrete surface coverage) to the values in the range set.
The gml:startPoint is the index position of a point in the grid that is mapped to the first point in the range set (this is also the index position of the first grid post). If the gml:startPoint property is omitted the gml:startPoint is assumed to be equal to the value of gml:low in the gml:Grid geometry. Subsequent points in the mapping are determined by the value of the gml:sequenceRule.
Simple Type AxisDirectionList
The different values in a gml:AxisDirectionList indicate the incrementation order to be used on all axes of the grid. Each axis shall be mentioned once and only once.
Simple Type AxisDirection
The value of a gml:AxisDirection indicates the incrementation order to be used on an axis of the grid.
Element MultiPointCoverage
In a gml:MultiPointCoverage the domain set is a gml:MultiPoint, that is a collection of arbitrarily distributed geometric points.
The content model is identical with gml:DiscreteCoverageType, but that gml:domainSet shall have values gml:MultiPoint.
In a gml:MultiPointCoverage the mapping from the domain to the range is straightforward.
- For gml:DataBlock encodings the points of the gml:MultiPoint are mapped in document order to the tuples of the data block.
- For gml:CompositeValue encodings the points of the gml:MultiPoint are mapped to the members of the composite value in document order.
- For gml:File encodings the points of the gml:MultiPoint are mapped to the records of the file in sequential order.
Element MultiCurveCoverage
In a gml:MultiCurveCoverage the domain is partioned into a collection of curves comprising a gml:MultiCurve. The coverage function then maps each curve in the collection to a value in the range set.
The content model is identical with gml:DiscreteCoverageType, but that gml:domainSet shall have values gml:MultiCurve.
In a gml:MultiCurveCoverage the mapping from the domain to the range is straightforward.
- For gml:DataBlock encodings the curves of the gml:MultiCurve are mapped in document order to the tuples of the data block.
- For gml:CompositeValue encodings the curves of the gml:MultiCurve are mapped to the members of the composite value in document order.
- For gml:File encodings the curves of the gml:MultiCurve are mapped to the records of the file in sequential order.
Element MultiSurfaceCoverage
In a gml:MultiSurfaceCoverage the domain is partioned into a collection of surfaces comprising a gml:MultiSurface. The coverage function than maps each surface in the collection to a value in the range set.
The content model is identical with gml:DiscreteCoverageType, but that gml:domainSet shall have values gml:MultiSurface.
In a gml:MultiSurfaceCoverage the mapping from the domain to the range is straightforward.
- For gml:DataBlock encodings the surfaces of the gml:MultiSurface are mapped in document order to the tuples of the data block.
- For gml:CompositeValue encodings the surfaces of the gml:MultiSurface are mapped to the members of the composite value in document order.
- For gml:File encodings the surfaces of the gml:MultiSurface are mapped to the records of the file in sequential order.
Element MultiSolidCoverage
In a gml:MultiSolidCoverage the domain is partioned into a collection of solids comprising a gml:MultiSolid. The coverage function than maps each solid in the collection to a value in the range set.
The content model is identical with gml:DiscreteCoverageType, but that gml:domainSet shall have values gml:MultiSolid.
In a gml:MultiSolidCoverage the mapping from the domain to the range is straightforward.
- For gml:DataBlock encodings the solids of the gml:MultiSolid are mapped in document order to the tuples of the data block.
- For gml:CompositeValue encodings the solids of the gml:MultiSolid are mapped to the members of the composite value in document order.
- For gml:File encodings the solids of the gml:MultiSolid are mapped to the records of the file in sequential order.
Element GridCoverage
A gml:GriddedCoverage is a discrete point coverage in which the domain set is a geometric grid of points.
Note that this is the same as the gml:MultiPointCoverage except that we have a gml:Grid to describe the domain.
The simple gridded coverage is not geometrically referenced and hence no geometric positions are assignable to the points in the grid. Such geometric positioning is introduced in the gml:RectifiedGridCoverage.
Element RectifiedGridCoverage
The gml:RectifiedGridCoverage is a discrete point coverage based on a rectified grid. It is similar to the grid coverage except that the points of the grid are geometrically referenced. The rectified grid coverage has a domain that is a gml:RectifiedGrid geometry.
Element Category
A gml:Category has an optional XML attribute codeSpace, whose value is a URI which identifies a dictionary, codelist or authority for the term.
Element Quantity
An XML attribute uom ("unit of measure") is required, whose value is a URI which identifies the definition of a ratio scale or units by which the numeric value shall be multiplied, or an interval or position scale on which the value occurs.
Element AbstractValue
gml:AbstractValue is an abstract element which acts as the head of a substitution group which contains gml:AbstractScalarValue, gml:AbstractScalarValueList, gml:CompositeValue and gml:ValueExtent, and (transitively) the elements in their substitution groups.
These elements may be used in an application schema as variables, so that in an XML instance document any member of its substitution group may occur.
Element AbstractScalarValue
gml:AbstractScalarValue is an abstract element which acts as the head of a substitution group which contains gml:Boolean, gml:Category, gml:Count and gml:Quantity, and (transitively) the elements in their substitution groups.
Element AbstractScalarValueList
gml:AbstractScalarValueList is an abstract element which acts as the head of a substitution group which contains gml:BooleanList, gml:CategoryList, gml:CountList and gml:QuantityList, and (transitively) the elements in their substitution groups.
Element valueProperty
Property that refers to, or contains, a Value. Convenience element for general use.
Element valueComponent
Property that refers to, or contains, a Value.
Element valueComponents
Property that contains Values.
Element CompositeValue
gml:CompositeValue is an aggregate value built from other values . It contains zero or an arbitrary number of gml:valueComponent elements, and zero or one gml:valueComponents property elements. It may be used for strongly coupled aggregates (vectors, tensors) or for arbitrary collections of values.
Element ValueArray
A Value Array is used for homogeneous arrays of primitive and aggregate values.
The member values may be scalars, composites, arrays or lists.
ValueArray has the same content model as CompositeValue, but the member values shall be homogeneous. The element declaration contains a Schematron constraint which expresses this restriction precisely. Since the members are homogeneous, the gml:referenceSystem (uom, codeSpace) may be specified on the gml:ValueArray itself and inherited by all the members if desired.
Element Grid
The gml:Grid implicitly defines an unrectified grid, which is a network composed of two or more sets of curves in which the members of each set intersect the members of the other sets in an algorithmic way. The region of interest within the grid is given in terms of its gml:limits, being the grid coordinates of diagonally opposed corners of a rectangular region. gml:axisLabels is provided with a list of labels of the axes of the grid (gml:axisName has been deprecated). gml:dimension specifies the dimension of the grid.
The gml:limits element contains a single gml:GridEnvelope. The gml:low and gml:high property elements of the envelope are each integerLists, which are coordinate tuples, the coordinates being measured as offsets from the origin of the grid along each axis, of the diagonally opposing corners of a "rectangular" region of interest.
Element RectifiedGrid
A rectified grid is a grid for which there is an affine transformation between the grid coordinates and the coordinates of an external coordinate reference system. It is defined by specifying the position (in some geometric space) of the grid "origin" and of the vectors that specify the post locations.
Note that the grid limits (post indexes) and axis name properties are inherited from gml:GridType and that gml:RectifiedGrid adds a gml:origin property (contains or references a gml:Point) and a set of gml:offsetVector properties.
Element AbstractSingleCRS
gml:AbstractSingleCRS implements a coordinate reference system consisting of one coordinate system and one datum (as opposed to a Compound CRS).
Element AbstractGeneralDerivedCRS
gml:AbstractGeneralDerivedCRS is a coordinate reference system that is defined by its coordinate conversion from another coordinate reference system. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
Element conversion
gml:conversion is an association role to the coordinate conversion used to define the derived CRS.
Element CompoundCRS
gml:CompundCRS is a coordinate reference system describing the position of points through two or more independent coordinate reference systems. It is associated with a non-repeating sequence of two or more instances of SingleCRS.
Element componentReferenceSystem
The gml:componentReferenceSystem elements are an ordered sequence of associations to all the component coordinate reference systems included in this compound coordinate reference system. The gml:AggregationAttributeGroup should be used to specify that the gml:componentReferenceSystem properties are ordered.
Element ellipsoidalCS
gml:ellipsoidalCS is an association role to the ellipsoidal coordinate system used by this CRS.
Element cartesianCS
gml:cartesianCS is an association role to the Cartesian coordinate system used by this CRS.
Element sphericalCS
gml:sphericalCS is an association role to the spherical coordinate system used by this CRS.
Element geodeticDatum
gml:geodeticDatum is an association role to the geodetic datum used by this CRS.
Element VerticalCRS
gml:VerticalCRS is a 1D coordinate reference system used for recording heights or depths. Vertical CRSs make use of the direction of gravity to define the concept of height or depth, but the relationship with gravity may not be straightforward. By implication, ellipsoidal heights (h) cannot be captured in a vertical coordinate reference system. Ellipsoidal heights cannot exist independently, but only as an inseparable part of a 3D coordinate tuple defined in a geographic 3D coordinate reference system.
Element verticalCS
gml:verticalCS is an association role to the vertical coordinate system used by this CRS.
Element verticalDatum
gml:verticalDatum is an association role to the vertical datum used by this CRS.
Element ProjectedCRS
gml:ProjectedCRS is a 2D coordinate reference system used to approximate the shape of the earth on a planar surface, but in such a way that the distortion that is inherent to the approximation is carefully controlled and known. Distortion correction is commonly applied to calculated bearings and distances to produce values that are a close match to actual field values.
Element baseGeodeticCRS
gml:baseGeodeticCRS is an association role to the geodetic coordinate reference system used by this projected CRS.
Element DerivedCRS
gml:DerivedCRS is a single coordinate reference system that is defined by its coordinate conversion from another single coordinate reference system known as the base CRS. The base CRS can be a projected coordinate reference system, if this DerivedCRS is used for a georectified grid coverage as described in ISO 19123, Clause 8.
Element baseCRS
gml:baseCRS is an association role to the coordinate reference system used by this derived CRS.
Element derivedCRSType
The gml:derivedCRSType property describes the type of a derived coordinate reference system. The required codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
Element coordinateSystem
An association role to the coordinate system used by this CRS.
Element EngineeringCRS
gml:EngineeringCRS is a contextually local coordinate reference system which can be divided into two broad categories:
- earth-fixed systems applied to engineering activities on or near the surface of the earth;
- CRSs on moving platforms such as road vehicles, vessels, aircraft, or spacecraft, see ISO 19111 8.3.
Element cylindricalCS
gml:cylindricalCS is an association role to the cylindrical coordinate system used by this CRS.
Element linearCS
gml:linearCS is an association role to the linear coordinate system used by this CRS.
Element polarCS
gml:polarCS is an association role to the polar coordinate system used by this CRS.
Element userDefinedCS
gml:userDefinedCS is an association role to the user defined coordinate system used by this CRS.
Element engineeringDatum
gml:engineeringDatum is an association role to the engineering datum used by this CRS.
Element ImageCRS
gml:ImageCRS is an engineering coordinate reference system applied to locations in images. Image coordinate reference systems are treated as a separate sub-type because the definition of the associated image datum contains two attributes not relevant to other engineering datums.
Element affineCS
gml:affineCS is an association role to the affine coordinate system used by this CRS.
Element imageDatum
gml:imageDatum is an association role to the image datum used by this CRS.
Element TemporalCRS
gml:TemporalCRS is a 1D coordinate reference system used for the recording of time.
Element timeCS
gml:timeCS is an association role to the time coordinate system used by this CRS.
Element temporalDatum
gml:temporalDatum is an association role to the temporal datum used by this CRS.
Element CoordinateSystemAxis
gml:CoordinateSystemAxis is a definition of a coordinate system axis.
Attribute uom
The uom attribute provides an identifier of the unit of measure used for this coordinate system axis. The value of this coordinate in a coordinate tuple shall be recorded using this unit of measure, whenever those coordinates use a coordinate reference system that uses a coordinate system that uses this axis.
Element axisAbbrev
gml:axisAbbrev is the abbreviation used for this coordinate system axis; this abbreviation is also used to identify the coordinates in the coordinate tuple. The codeSpace attribute may reference a source of more information on a set of standardized abbreviations, or on this abbreviation.
Element axisDirection
gml:axisDirection is the direction of this coordinate system axis (or in the case of Cartesian projected coordinates, the direction of this coordinate system axis at the origin).
Within any set of coordinate system axes, only one of each pair of terms may be used. For earth-fixed CRSs, this direction is often approximate and intended to provide a human interpretable meaning to the axis. When a geodetic datum is used, the precise directions of the axes may therefore vary slightly from this approximate direction.
The codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
Element minimumValue
The gml:minimumValue and gml:maximumValue properties allow the specification of minimum and maximum value normally allowed for this axis, in the unit of measure for the axis. For a continuous angular axis such as longitude, the values wrap-around at this value. Also, values beyond this minimum/maximum can be used for specified purposes, such as in a bounding box. A value of minus infinity shall be allowed for the gml:minimumValue element, a value of plus infiniy for the gml:maximumValue element. If these elements are omitted, the value is unspecified.
Element maximumValue
The gml:minimumValue and gml:maximumValue properties allow the specification of minimum and maximum value normally allowed for this axis, in the unit of measure for the axis. For a continuous angular axis such as longitude, the values wrap-around at this value. Also, values beyond this minimum/maximum can be used for specified purposes, such as in a bounding box. A value of minus infinity shall be allowed for the gml:minimumValue element, a value of plus infiniy for the gml:maximumValue element. If these elements are omitted, the value is unspecified.
Element rangeMeaning
gml:rangeMeaning describes the meaning of axis value range specified by gml:minimumValue and gml:maximumValue. This element shall be omitted when both gml:minimumValue and gml:maximumValue are omitted. This element should be included when gml:minimumValue and/or gml:maximumValue are included. If this element is omitted when the gml:minimumValue and/or gml:maximumValue are included, the meaning is unspecified. The codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
Element AbstractCoordinateSystem
gml:AbstractCoordinateSystem is a coordinate system (CS) is the non-repeating sequence of coordinate system axes that spans a given coordinate space. A CS is derived from a set of mathematical rules for specifying how coordinates in a given space are to be assigned to points. The coordinate values in a coordinate tuple shall be recorded in the order in which the coordinate system axes associations are recorded. This abstract complex type shall not be used, extended, or restricted, in an Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
Element axis
The gml:axis property is an association role (ordered sequence) to the coordinate system axes included in this coordinate system. The coordinate values in a coordinate tuple shall be recorded in the order in which the coordinate system axes associations are recorded, whenever those coordinates use a coordinate reference system that uses this coordinate system. The gml:AggregationAttributeGroup should be used to specify that the axis objects are ordered.
Element EllipsoidalCS
gml:EllipsoidalCS is a two- or three-dimensional coordinate system in which position is specified by geodetic latitude, geodetic longitude, and (in the three-dimensional case) ellipsoidal height. An EllipsoidalCS shall have two or three gml:axis property elements; the number of associations shall equal the dimension of the CS.
Element CartesianCS
gml:CartesianCS is a 1-, 2-, or 3-dimensional coordinate system. In the 1-dimensional case, it contains a single straight coordinate axis. In the 2- and 3-dimensional cases gives the position of points relative to orthogonal straight axes. In the multi-dimensional case, all axes shall have the same length unit of measure. A CartesianCS shall have one, two, or three gml:axis property elements.
Element VerticalCS
gml:VerticalCS is a one-dimensional coordinate system used to record the heights or depths of points. Such a coordinate system is usually dependent on the Earth's gravity field, perhaps loosely as when atmospheric pressure is the basis for the vertical coordinate system axis. A VerticalCS shall have one gml:axis property element.
Element TimeCS
gml:TimeCS is a one-dimensional coordinate system containing a time axis, used to describe the temporal position of a point in the specified time units from a specified time origin. A TimeCS shall have one gml:axis property element.
Element LinearCS
gml:LinearCS is a one-dimensional coordinate system that consists of the points that lie on the single axis described. The associated coordinate is the distance – with or without offset – from the specified datum to the point along the axis. A LinearCS shall have one gml:axis property element.
Element UserDefinedCS
gml:UserDefinedCS is a two- or three-dimensional coordinate system that consists of any combination of coordinate axes not covered by any other coordinate system type. A UserDefinedCS shall have two or three gml:axis property elements; the number of property elements shall equal the dimension of the CS.
Element SphericalCS
gml:SphericalCS is a three-dimensional coordinate system with one distance measured from the origin and two angular coordinates. A SphericalCS shall have three gml:axis property elements.
Element PolarCS
gml:PolarCS ia s two-dimensional coordinate system in which position is specified by the distance from the origin and the angle between the line from the origin to a point and a reference direction. A PolarCS shall have two gml:axis property elements.
Element CylindricalCS
gml:CylindricalCS is a three-dimensional coordinate system consisting of a polar coordinate system extended by a straight coordinate axis perpendicular to the plane spanned by the polar coordinate system. A CylindricalCS shall have three gml:axis property elements.
Element AffineCS
gml:AffineCS is a two- or three-dimensional coordinate system with straight axes that are not necessarily orthogonal. An AffineCS shall have two or three gml:axis property elements; the number of property elements shall equal the dimension of the CS.
Element AbstractCRS
gml:AbstractCRS specifies a coordinate reference system which is usually single but may be compound. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
Element domainOfValidity
The gml:domainOfValidity property implements an association role to an EX_Extent object as encoded in ISO/TS 19139, either referencing or containing the definition of that extent.
Element scope
The gml:scope property provides a description of the usage, or limitations of usage, for which this CRS-related object is valid. If unknown, enter "not known".
Element AbstractDatum
A gml:AbstractDatum specifies the relationship of a coordinate system to the earth, thus creating a coordinate reference system. A datum uses a parameter or set of parameters that determine the location of the origin of the coordinate reference system. Each datum subtype may be associated with only specific types of coordinate systems. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
Element anchorDefinition
gml:anchorDefinition is a description, possibly including coordinates, of the definition used to anchor the datum to the Earth. Also known as the "origin", especially for engineering and image datums. The codeSpace attribute may be used to reference a source of more detailed on this point or surface, or on a set of such descriptions.
- For a geodetic datum, this point is also known as the fundamental point, which is traditionally the point where the relationship between geoid and ellipsoid is defined. In some cases, the "fundamental point" may consist of a number of points. In those cases, the parameters defining the geoid/ellipsoid relationship have been averaged for these points, and the averages adopted as the datum definition.
- For an engineering datum, the anchor definition may be a physical point, or it may be a point with defined coordinates in another CRS.may
- For an image datum, the anchor definition is usually either the centre of the image or the corner of the image.
- For a temporal datum, this attribute is not defined. Instead of the anchor definition, a temporal datum carries a separate time origin of type DateTime.
Element realizationEpoch
gml:realizationEpoch is the time after which this datum definition is valid. See ISO 19111 Table 32 for details.
Element GeodeticDatum
gml:GeodeticDatum is a geodetic datum defines the precise location and orientation in 3-dimensional space of a defined ellipsoid (or sphere), or of a Cartesian coordinate system centered in this ellipsoid (or sphere).
Element primeMeridian
gml:primeMeridian is an association role to the prime meridian used by this geodetic datum.
Element ellipsoid
gml:ellipsoid is an association role to the ellipsoid used by this geodetic datum.
Element Ellipsoid
A gml:Ellipsoid is a geometric figure that may be used to describe the approximate shape of the earth. In mathematical terms, it is a surface formed by the rotation of an ellipse about its minor axis.
Element semiMajorAxis
gml:semiMajorAxis specifies the length of the semi-major axis of the ellipsoid, with its units. Uses the MeasureType with the restriction that the unit of measure referenced by uom must be suitable for a length, such as metres or feet.
Element secondDefiningParameter
gml:secondDefiningParameter is a property containing the definition of the second parameter that defines the shape of an ellipsoid. An ellipsoid requires two defining parameters: semi-major axis and inverse flattening or semi-major axis and semi-minor axis. When the reference body is a sphere rather than an ellipsoid, only a single defining parameter is required, namely the radius of the sphere; in that case, the semi-major axis "degenerates" into the radius of the sphere.
The inverseFlattening element contains the inverse flattening value of the ellipsoid. This value is a scale factor (or ratio). It uses gml:LengthType with the restriction that the unit of measure referenced by the uom attribute must be suitable for a scale factor, such as percent, permil, or parts-per-million.
The semiMinorAxis element contains the length of the semi-minor axis of the ellipsoid. When the isSphere element is included, the ellipsoid is degenerate and is actually a sphere. The sphere is completely defined by the semi-major axis, which is the radius of the sphere.
Element PrimeMeridian
A gml:PrimeMeridian defines the origin from which longitude values are determined. The default value for the prime meridian gml:identifier value is "Greenwich".
Element greenwichLongitude
gml:greenwichLongitude is the longitude of the prime meridian measured from the Greenwich meridian, positive eastward. If the value of the prime meridian "name" is "Greenwich" then the value of greenwichLongitude shall be 0 degrees.
Element EngineeringDatum
gml:EngineeringDatum defines the origin of an engineering coordinate reference system, and is used in a region around that origin. This origin may be fixed with respect to the earth (such as a defined point at a construction site), or be a defined point on a moving vehicle (such as on a ship or satellite).
Element ImageDatum
gml:ImageDatum defines the origin of an image coordinate reference system, and is used in a local context only. For an image datum, the anchor definition is usually either the centre of the image or the corner of the image. For more information, see ISO 19111 B.3.5.
Element pixelInCell
gml:pixelInCell is a specification of the way an image grid is associated with the image data attributes. The required codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
Element VerticalDatum
gml:VerticalDatum is a textual description and/or a set of parameters identifying a particular reference level surface used as a zero-height surface, including its position with respect to the Earth for any of the height types recognized by this International Standard.
Element TemporalDatum
A gml:TemporalDatum defines the origin of a Temporal Reference System. This type omits the "anchorDefinition" and "realizationEpoch" elements and adds the "origin" element with the dateTime type.
Element origin
gml:origin is the date and time origin of this temporal datum.
Element AbstractCoordinateOperation
gml:AbstractCoordinateOperation is a mathematical operation on coordinates that transforms or converts coordinates to another coordinate reference system. Many but not all coordinate operations (from CRS A to CRS B) also uniquely define the inverse operation (from CRS B to CRS A). In some cases, the operation method algorithm for the inverse operation is the same as for the forward algorithm, but the signs of some operation parameter values shall be reversed. In other cases, different algorithms are required for the forward and inverse operations, but the same operation parameter values are used. If (some) entirely different parameter values are needed, a different coordinate operation shall be defined.
The optional coordinateOperationAccuracy property elements provide estimates of the impact of this coordinate operation on point position accuracy.
Element operationVersion
gml:operationVersion is the
version of the coordinate transformation (i.e., instantiation due to the stochastic nature of the parameters). Mandatory when describing a transformation, and should not be supplied for a conversion.
Element coordinateOperationAccuracy
gml:coordinateOperationAccuracy is an association role to a DQ_PositionalAccuracy object as encoded in ISO/TS 19139, either referencing or containing the definition of that positional accuracy. That object contains an estimate of the impact of this coordinate operation on point accuracy. That is, it gives position error estimates for the target coordinates of this coordinate operation, assuming no errors in the source coordinates.
Element sourceCRS
gml:sourceCRS is an association role to the source CRS (coordinate reference system) of this coordinate operation.
Element targetCRS
gml:targetCRS is an association role to the target CRS (coordinate reference system) of this coordinate operation.
Element AbstractSingleOperation
gml:AbstractSingleOperation is a single (not concatenated) coordinate operation.
Element AbstractGeneralConversion
gm:AbstractGeneralConversion is an abstract operation on coordinates that does not include any change of datum. The best-known example of a coordinate conversion is a map projection. The parameters describing coordinate conversions are defined rather than empirically derived. Note that some conversions have no parameters. The operationVersion, sourceCRS, and targetCRS elements are omitted in a coordinate conversion.
This abstract complex type is expected to be extended for well-known operation methods with many Conversion instances, in GML Application Schemas that define operation-method-specialized element names and contents. This conversion uses an operation method, usually with associated parameter values. However, operation methods and parameter values are directly associated with concrete subtypes, not with this abstract type. All concrete types derived from this type shall extend this type to include a "usesMethod" element that references the "OperationMethod" element. Similarly, all concrete types derived from this type shall extend this type to include zero or more elements each named "uses...Value" that each use the type of an element substitutable for the "AbstractGeneralParameterValue" element.
Element AbstractGeneralTransformation
gml:AbstractGeneralTransformation is an abstract operation on coordinates that usually includes a change of Datum. The parameters of a coordinate transformation are empirically derived from data containing the coordinates of a series of points in both coordinate reference systems. This computational process is usually "over-determined", allowing derivation of error (or accuracy) estimates for the transformation. Also, the stochastic nature of the parameters may result in multiple (different)
versions of the same coordinate transformation. The operationVersion, sourceCRS, and targetCRS proeprty elements are mandatory in a coordinate transformation.
This abstract complex type is expected to be extended for well-known operation methods with many Transformation instances, in Application Schemas that define operation-method-specialized value element names and contents. This transformation uses an operation method with associated parameter values. However, operation methods and parameter values are directly associated with concrete subtypes, not with this abstract type. All concrete types derived from this type shall extend this type to include a "usesMethod" element that references one "OperationMethod" element. Similarly, all concrete types derived from this type shall extend this type to include one or more elements each named "uses...Value" that each use the type of an element substitutable for the "AbstractGeneralParameterValue" element.
Element coordOperation
gml:coordOperation is an association role to a coordinate operation.
Element PassThroughOperation
gml:PassThroughOperation is a pass-through operation specifies that a subset of a coordinate tuple is subject to a specific coordinate operation.
The modifiedCoordinate property elements are an ordered sequence of positive integers defining the positions in a coordinate tuple of the coordinates affected by this pass-through operation. The AggregationAttributeGroup should be used to specify that the modifiedCoordinate elements are ordered.
Element modifiedCoordinate
gml:modifiedCoordinate is a positive integer defining a position in a coordinate tuple.
Element Conversion
gml:Conversion is a concrete operation on coordinates that does not include any change of Datum. The best-known example of a coordinate conversion is a map projection. The parameters describing coordinate conversions are defined rather than empirically derived. Note that some conversions have no parameters.
This concrete complex type can be used without using a GML Application Schema that defines operation-method-specialized element names and contents, especially for methods with only one Conversion instance.
The usesValue property elements are an unordered list of composition associations to the set of parameter values used by this conversion operation.
Element method
gml:method is an association role to the operation method used by a coordinate operation.
Element parameterValue
gml:parameterValue is a composition association to a parameter value or group of parameter values used by a coordinate operation.
Element Transformation
gml:Transformation is a concrete object element derived from gml:GeneralTransformation (13.6.2.13).
This concrete object can be used for all operation methods, without using a GML Application Schema that defines operation-method-specialized element names and contents, especially for methods with only one Transformation instance.
The parameterValue elements are an unordered list of composition associations to the set of parameter values used by this conversion operation.
Element AbstractGeneralParameterValue
gml:AbstractGeneralParameterValue is an abstract parameter value or group of parameter values.
This abstract complexType is expected to be extended and restricted for well-known operation methods with many instances, in Application Schemas that define operation-method-specialized element names and contents. Specific parameter value elements are directly contained in concrete subtypes, not in this abstract type. All concrete types derived from this type shall extend this type to include one "...Value" element with an appropriate type, which should be one of the element types allowed in the ParameterValueType. In addition, all derived concrete types shall extend this type to include a "operationParameter" property element that references one element substitutable for the "OperationParameter" object element.
Element ParameterValue
gml:ParameterValue is a parameter value, an ordered sequence of values, or a reference to a file of parameter values. This concrete complex type may be used for operation methods without using an Application Schema that defines operation-method-specialized element names and contents, especially for methods with only one instance. This complex type may be used, extended, or restricted for well-known operation methods, especially for methods with many instances.
Element value
gml:value is a numeric value of an operation parameter, with its associated unit of measure.
Element stringValue
gml:stringValue is a character string value of an operation parameter. A string value does not have an associated unit of measure.
Element integerValue
gml:integerValue is a positive integer value of an operation parameter, usually used for a count. An integer value does not have an associated unit of measure.
Element booleanValue
gml:booleanValue is a boolean value of an operation parameter. A Boolean value does not have an associated unit of measure.
Element valueList
gml:valueList is an ordered sequence of two or more numeric values of an operation parameter list, where each value has the same associated unit of measure. An element of this type contains a space-separated sequence of double values.
Element integerValueList
gml:integerValueList is an ordered sequence of two or more integer values of an operation parameter list, usually used for counts. These integer values do not have an associated unit of measure. An element of this type contains a space-separated sequence of integer values.
Element valueFile
gml:valueFile is a reference to a file or a part of a file containing one or more parameter values, each numeric value with its associated unit of measure. When referencing a part of a file, that file shall contain multiple identified parts, such as an XML encoded document. Furthermore, the referenced file or part of a file may reference another part of the same or different files, as allowed in XML documents.
Element operationParameter
gml:operationParameter is an association role to the operation parameter of which this is a value.
Element ParameterValueGroup
gml:ParameterValueGroup is a group of related parameter values. The same group can be repeated more than once in a Conversion, Transformation, or higher level ParameterValueGroup, if those instances contain different values of one or more parameterValues which suitably distinquish among those groups. This concrete complex type can be used for operation methods without using an Application Schema that defines operation-method-specialized element names and contents. This complex type may be used, extended, or restricted for well-known operation methods, especially for methods with only one instance.
The parameterValue elements are an unordered set of composition association roles to the parameter values and groups of values included in this group.
Element group
gml:group is an association role to the operation parameter group for which this element provides parameter values.
Element OperationMethod
gml:OperationMethod is a method (algorithm or procedure) used to perform a coordinate operation. Most operation methods use a number of operation parameters, although some coordinate conversions use none. Each coordinate operation using the method assigns values to these parameters.
The parameter elements are an unordered list of associations to the set of operation parameters and parameter groups used by this operation method.
Element formulaCitation
gml:formulaCitation provides a reference to a publication giving the formula(s) or procedure used by an coordinate operation method.
Element formula
gml:formula Formula(s) or procedure used by an operation method. The use of the codespace attribite has been deprecated. The property value shall be a character string.
Element sourceDimensions
gml:sourceDimensions is the number of dimensions in the source CRS of this operation method.
Element targetDimensions
gml:targetDimensions is the number of dimensions in the target CRS of this operation method.
Element parameter
gml:parameter is an association to an operation parameter or parameter group.
Element AbstractGeneralOperationParameter
gml:GeneralOperationParameter is the abstract definition of a parameter or group of parameters used by an operation method.
Element minimumOccurs
gml:minimumOccurs is the minimum number of times that values for this parameter group or parameter are required. If this attribute is omitted, the minimum number shall be one.
Element OperationParameter
gml:OperationParameter is the definition of a parameter used by an operation method. Most parameter values are numeric, but other types of parameter values are possible. This complex type is expected to be used or extended for all operation methods, without defining operation-method-specialized element names.
Element OperationParameterGroup
gml:OperationParameterGroup is the definition of a group of parameters used by an operation method. This complex type is expected to be used or extended for all applicable operation methods, without defining operation-method-specialized element names.
The generalOperationParameter elements are an unordered list of associations to the set of operation parameters that are members of this group.
Element maximumOccurs
gml:maximumOccurs is the maximum number of times that values for this parameter group may be included. If this attribute is omitted, the maximum number shall be one.
Element Observation
The content model is a straightforward extension of gml:AbstractFeatureType; it automatically has the gml:identifier, gml:description, gml:descriptionReference, gml:name, and gml:boundedBy properties.
The gml:validTime element describes the time of the observation. Note that this may be a time instant or a time period.
The gml:using property contains or references a description of a sensor, instrument or procedure used for the observation.
The gml:target property contains or references the specimen, region or station which is the object of the observation. This property is particularly useful for remote observations, such as photographs, where a generic location property might apply to the location of the camera or the location of the field of view, and thus may be ambiguous.
The gml:subject element is provided as a convenient synonym for gml:target. This is the term commonly used in phtotography.
The gml:resultOf property indicates the result of the observation. The value may be inline, or a reference to a value elsewhere.
Element DirectedObservation
A gml:DirectedObservation is the same as an observation except that it adds an additional gml:direction property. This is the direction in which the observation was acquired. Clearly this applies only to certain types of observations such as visual observations by people, or observations obtained from terrestrial cameras.
Element DirectedObservationAtDistance
gml:DirectedObservationAtDistance adds an additional distance property. This is the distance from the observer to the subject of the observation. Clearly this applies only to certain types of observations such as visual observations by people, or observations obtained from terrestrial cameras.
Element TimeReferenceSystem
A reference system is characterized in terms of its domain of validity: the spatial and temporal extent over which it is applicable. The basic GML element for temporal reference systems is gml:TimeReferenceSystem. Its content model extends gml:DefinitionType with one additional property, gml:domainOfValidity.
Element TimeCoordinateSystem
A temporal coordinate system shall be based on a continuous interval scale defined in terms of a single time interval.
The differences to ISO 19108 TM_CoordinateSystem are:
- the origin is specified either using the property gml:originPosition whose value is a direct time position, or using the property gml:origin whose model is gml:TimeInstantPropertyType; this permits more flexibility in representation and also supports referring to a value fixed elsewhere;
- the interval uses gml:TimeIntervalLengthType.
Element TimeCalendar
A calendar is a discrete temporal reference system that provides a basis for defining temporal position to a resolution of one day.
gml:TimeCalendar adds one property to those inherited from gml:TimeReferenceSystem. A gml:referenceFrame provides a link to a gml:TimeCalendarEra that it uses. A gml:TimeCalendar may reference more than one calendar era.
The referenceFrame element follows the standard GML property model, allowing the association to be instantiated either using an inline description using the gml:TimeCalendarEra element, or a link to a gml:TimeCalendarEra which is explicit elsewhere.
Element TimeCalendarEra
gml:TimeCalendarEra inherits basic properties from gml:DefinitionType and has the following additional properties:
- gml:referenceEvent is the name or description of a mythical or historic event which fixes the position of the base scale of the calendar era. This is given as text or using a link to description held elsewhere.
- gml:referenceDate specifies the date of the referenceEvent expressed as a date in the given calendar. In most calendars, this date is the origin (i.e., the first day) of the scale, but this is not always true.
- gml:julianReference specifies the Julian date that corresponds to the reference date. The Julian day number is an integer value; the Julian date is a decimal value that allows greater resolution. Transforming calendar dates to and from Julian dates provides a relatively simple basis for transforming dates from one calendar to another.
- gml:epochOfUse is the period for which the calendar era was used as a basis for dating.
Element TimeClock
A clock provides a basis for defining temporal position within a day. A clock shall be used with a calendar in order to provide a complete description of a temporal position within a specific day.
gml:TimeClock adds the following properties to those inherited from gml:TimeReferenceSystemType:
- gml:referenceEvent is the name or description of an event, such as solar noon or sunrise, which fixes the position of the base scale of the clock.
- gml:referenceTime specifies the time of day associated with the reference event expressed as a time of day in the given clock. The reference time is usually the origin of the clock scale.
- gml:utcReference specifies the 24 hour local or UTC time that corresponds to the reference time.
- gml:dateBasis contains or references the calendars that use this clock.
Element TimeOrdinalReferenceSystem
In some applications of geographic information — such as geology and archaeology — relative position in time is known more precisely than absolute time or duration. The order of events in time can be well established, but the magnitude of the intervals between them cannot be accurately determined; in such cases, the use of an ordinal temporal reference system is appropriate. An ordinal temporal reference system is composed of a sequence of named coterminous eras, which may in turn be composed of sequences of member eras at a finer scale, giving the whole a hierarchical structure of eras of verying resolution.
An ordinal temporal reference system whose component eras are not further subdivided is effectively a temporal topological complex constrained to be a linear graph. An ordinal temporal reference system some or all of whose component eras are subdivided is effectively a temporal topological complex with the constraint that parallel branches may only be constructed in pairs where one is a single temporal ordinal era and the other is a sequence of temporal ordinal eras that are called "members" of the "group". This constraint means that within a single temporal ordinal reference system, the relative position of all temporal ordinal eras is unambiguous.
The positions of the beginning and end of a given era may calibrate the relative time scale.
gml:TimeOrdinalReferenceSystem adds one or more gml:component properties to the generic temporal reference system model.
Element TimeOrdinalEra
Its content model follows the pattern of gml:TimeEdge, inheriting standard properties from gml:DefinitionType, and adding gml:start, gml:end and gml:extent properties, a set of gml:member properties which indicate ordered gml:TimeOrdinalEra elements, and a gml:group property which points to the parent era.
The recursive inclusion of gml:TimeOrdinalEra elements allow the construction of an arbitrary depth hierarchical ordinal reference schema, such that an ordinal era at a given level of the hierarchy includes a sequence of shorter, coterminous ordinal eras.
Element AbstractTimeTopologyPrimitive
gml:TimeTopologyPrimitive acts as the head of a substitution group for topological temporal primitives.
Temporal topology primitives shall imply the ordering information between features or feature properties. The temporal connection of features can be examined if they have temporal topology primitives as values of their properties. Usually, an instantaneous feature associates with a time node, and a static feature associates with a time edge. A feature with both modes associates with the temporal topology primitive: a supertype of time nodes and time edges.
A topological primitive is always connected to one or more other topological primitives, and is, therefore, always a member of a topological complex. In a GML instance, this will often be indicated by the primitives being described by elements that are descendents of an element describing a complex. However, in order to support the case where a temporal topological primitive is described in another context, the optional complex property is provided, which carries a reference to the parent temporal topological complex.
Element TimeTopologyComplex
A temporal topology complex shall be the connected acyclic directed graph composed of temporal topological primitives, i.e. time nodes and time edges. Because a time edge may not exist without two time nodes on its boundaries, static features have time edges from a temporal topology complex as the values of their temporal properties, regardless of explicit declarations.
A temporal topology complex expresses a linear or a non-linear graph. A temporal linear graph, composed of a sequence of time edges, provides a lineage described only by "substitution" of feature instances or feature element values. A time node as the start or the end of the graph connects with at least one time edge. A time node other than the start and the end shall connect to at least two time edges: one of starting from the node, and another ending at the node.
A temporal topological complex is a set of connected temporal topological primitives. The member primtives are indicated, either by reference or by value, using the primitive property.
Element TimeNode
A time node is a zero-dimensional topological primitive that represents an identifiable node in time (it is equivalent to a point in space). A node may act as the termination or initiation of any number of time edges. A time node may be realised as a geometry, its position, whose value is a time instant.
Element TimeEdge
A time edge is a one-dimensional topological primitive. It is an open interval that starts and ends at a node. The edge may be realised as a geometry whose value is a time period.
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See ISO/DIS 19136 15.6.
A number of types and relationships are defined to represent the time-varying properties of geographic features.
In a comprehensive treatment of spatiotemporal modeling, Langran (see Bibliography) distinguished three principal temporal entities: states, events, and evidence; the schema specified in the following Subclauses incorporates elements for each.
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See ISO/DIS 19136 Clause 9.
A GML feature is a (representation of a) identifiable real-world object in a selected domain of discourse. The feature schema provides a framework for the creation of GML features and feature collections.
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See ISO/DIS 19136 12.3.
Geometric aggregates (i.e. instances of a subtype of gml:AbstractGeometricAggregateType) are arbitrary aggregations of geometry elements. They are not assumed to have any additional internal structure and are used to "collect" pieces of geometry of a specified type. Application schemas may use aggregates for features that use multiple geometric objects in their representations.
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See ISO/DIS 19136 Clause 11.
Beside the "simple" geometric primitives specified in the previous Clause, this Clause specifies additional primitives to describe real world situations which require a more expressive geometry model.
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See ISO/DIS 19136 Clause 10.
GML is an OGC Standard.
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See ISO/DIS 19136 Clause 10.
Any geometry element that inherits the semantics of AbstractGeometryType may be viewed as a set of direct positions.
All of the classes derived from AbstractGeometryType inherit an optional association to a coordinate reference system. All direct positions shall directly or indirectly be associated with a coordinate reference system. When geometry elements are aggregated in another geometry element (such as a MultiGeometry or GeometricComplex), which already has a coordinate reference system specified, then these elements are assumed to be in that same coordinate reference system unless otherwise specified.
The geometry model distinguishes geometric primitives, aggregates and complexes.
Geometric primitives, i.e. instances of a subtype of AbstractGeometricPrimitiveType, will be open, that is, they will not contain their boundary points; curves will not contain their end points, surfaces will not contain their boundary curves, and solids will not contain their bounding surfaces.
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See ISO/DIS 19136 17.3.
gml:MeasureType is defined in the basicTypes schema. The measure types defined here correspond with a set of convenience measure types described in ISO/TS 19103. The XML implementation is based on the XML Schema simple type "double" which supports both decimal and scientific notation, and includes an XML attribute "uom" which refers to the units of measure for the value. Note that, there is no requirement to store values using any particular format, and applications receiving elements of this type may choose to coerce the data to any other type as convenient.
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See ISO/DIS 17.2.
Several GML Schema components concern or require a reference scale or units of measure. Units are required for quantities that may occur as values of properties of feature types, as the results of observations, in the range parameters of a coverage, and for measures used in Coordinate Reference System definitions.
The basic unit definition is an extension of the general gml:Definition element defined in 16.2.1. Three specialized elements for unit definition are further derived from this.
This model is based on the SI system of units [ISO 1000], which distinguishes between Base Units and Derived Units.
- Base Units are the preferred units for a set of orthogonal fundamental quantities which define the particular system of units, which may not be derived by combination of other base units.
- Derived Units are the preferred units for other quantities in the system, which may be defined by algebraic combination of the base units.
In some application areas Conventional units are used, which may be converted to the preferred units using a scaling factor or a formula which defines a re-scaling and offset. The set of preferred units for all physical quantity types in a particular system of units is composed of the union of its base units and derived units.
Unit definitions are substitutable for the gml:Definition element declared as part of the dictionary model. A dictionary that contains only unit definitions and references to unit definitions is a units dictionary.
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See ISO/DIS 19136 Clause 16.
Many applications require definitions of terms which are used within instance documents as the values of certain properties or as reference information to tie properties to standard information values in some way. Units of measure and descriptions of measurable phenomena are two particular examples.
It will often be convenient to use definitions provided by external authorities. These may already be packaged for delivery in various ways, both online and offline. In order that they may be referred to from GML documents it is generally necessary that a URI be available for each definition. Where this is the case then it is usually preferable to refer to these directly.
Alternatively, it may be convenient or necessary to capture definitions in XML , either embedded within an instance document containing features or as a separate document. The definitions may be transcriptions from an external source, or may be new definitions for a local purpose. In order to support this case, some simple components are provided in GML in the form of
- a generic gml:Definition, which may serve as the basis for more specialized definitions
- a generic gml:Dictionary, which allows a set of definitions or references to definitions to be collected
These components may be used directly, but also serve as the basis for more specialised definition elements in GML, in particular: coordinate operations, coordinate reference systems, datums, temporal reference systems, and units of measure.
Note that the GML definition and dictionary components implement a simple nested hierarchy of definitions with identifiers. The latter provide handles which may be used in the description of more complex relationships between terms. However, the GML dictionary components are not intended to provide direct support for complex taxonomies, ontologies or thesauri. Specialised XML tools are available to satisfy the more sophisticated requirements.
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See ISO/DIS 19136 7.2.
The gmlBase schema components establish the GML model and syntax, in particular
- a root XML type from which XML types for all GML objects should be derived,
- a pattern and components for GML properties,
- patterns for collections and arrays, and components for generic collections and arrays,
- components for associating metadata with GML objects,
- components for constructing definitions and dictionaries.
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See ISO/DIS 19136 8.2.
W3C XML Schema provides a set of built-in "simple" types which define methods for representing values as literals without internal markup. These are described in W3C XML Schema Part 2:2001. Because GML is an XML encoding in which instances are described using XML Schema, these simple types shall be used as far as possible and practical for the representation of data types. W3C XML Schema also provides methods for defining
- new simple types by restriction and combination of the built-in types, and
- complex types, with simple content, but which also have XML attributes.
In many places where a suitable built-in simple type is not available, simple content types derived using the XML Schema mechanisms are used for the representation of data types in GML.
A set of these simple content types that are required by several GML components are defined in the basicTypes schema, as well as some elements based on them. These are primarily based around components needed to record amounts, counts, flags and terms, together with support for exceptions or null values.
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See ISO/DIS 19136 15.2.
The GML temporal schemas include components for describing temporal geometry and topology, temporal reference systems, and the temporal characteristics of geographic data. The model underlying the representation constitutes a profile of the conceptual schema described in ISO 19108. The underlying spatiotemporal model strives to accommodate both feature-level and attribute-level time stamping; basic support for tracking moving objects is also included.
Time is measured on two types of scales: interval and ordinal. An interval scale offers a basis for measuring duration, an ordinal scale provides information only about relative position in time.
Two other ISO standards are relevant to describing temporal objects: ISO 8601 describes encodings for time instants and time periods, as text strings with particular structure and punctuation; ISO 11404 provides a detailed description of time intervals as part of a general discussion of language independent datatypes.
The temporal schemas cover two interrelated topics and provide basic schema components for representing temporal instants and periods, temporal topology, and reference systems; more specialized schema components defines components used for dynamic features. Instances of temporal geometric types are used as values for the temporal properties of geographic features.
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See ISO/DIS 19136 Clause 18.
The direction schema components provide the GML Application Schema developer with a standard property element to describe direction, and associated objects that may be used to express orientation, direction, heading, bearing or other directional aspects of geographic features.
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See ISO/DIS 19136 Clause 14.
Topology is the branch of mathematics describing the properties of objects which are invariant under continuous deformation. For example, a circle is topologically equivalent to an ellipse because one can be transformed into the other by stretching. In geographic modelling, the foremost use of topology is in accelerating computational geometry. The constructs of topology allow characterisation of the spatial relationships between objects using simple combinatorial or algebraic algorithms. Topology, realised by the appropriate geometry, also allows a compact and unambiguous mechanism for expressing shared geometry among geographic features.
There are four instantiable classes of primitive topology objects, one for each dimension up to 3D. In addition, topological complexes are supported, too.
There is strong symmetry in the (topological boundary and coboundary) relationships between topology primitives of adjacent dimensions. Topology primitives are bounded by directed primitives of one lower dimension. The coboundary of each topology primitive is formed from directed topology primitives of one higher dimension.
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See ISO/DIS 19136 12.2.
Geometric complexes (i.e. instances of gml:GeometricComplexType) are closed collections of geometric primitives, i.e. they will contain their boundaries.
A geometric complex (gml:GeometricComplex) is defined by ISO 19107:2003, 6.6.1 as "a set of primitive geometric objects (in a common coordinate system) whose interiors are disjoint. Further, if a primitive is in a geometric complex, then there exists a set of primitives in that complex whose point-wise union is the boundary of this first primitive."
A geometric composite (gml:CompositeCurve, gml:CompositeSurface and gml:CompositeSolid) represents a geometric complex with an underlying core geometry that is isomorphic to a primitive, i.e. it can be viewed as a primitive and as a complex. See ISO 19107:2003, 6.1 and 6.6.3 for more details on the nature of composite geometries.
Geometric complexes and composites are intended to be used in application schemas where the sharing of geometry is important.
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See ISO/DIS 19136 20.3.
A coverage incorporates a mapping from a spatiotemporal domain to a range set, the latter providing the set in which the attribute values live. The range set may be an arbitrary set including discrete lists, integer or floating point ranges, and multi-dimensional vector spaces.
A coverage can be viewed as the graph of the coverage function f:A à B, that is as the set of ordered pairs {(x, f(x)) | where x is in A}. This view is especially applicable to the GML encoding of a coverage. In the case of a discrete coverage, the domain set A is partitioned into a collection of subsets (typically a disjoint collection) A = UAi and the function f is constant on each Ai. For a spatial domain, the Ai are geometry elements, hence the coverage can be viewed as a collection of (geometry,value) pairs, where the value is an element of the range set. If the spatial domain A is a topological space then the coverage can be viewed as a collection of (topology,value) pairs, where the topology element in the pair is a topological n-chain (in GML terms this is a gml:TopoPoint, gml:TopoCurve, gml:TopoSurface or gml:TopoSolid).
A coverage is implemented as a GML feature. We can thus speak of a "temperature distribution feature", or a "remotely sensed image feature", or a "soil distribution feature".
As is the case for any GML object, a coverage object may also be the value of a property of a feature.
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See ISO/DIS 19136 17.5.
The elements declared in this Clause build on other GML schema components, in particular gml:AbstractTimeObject, gml:AbstractGeometry, and the following types: gml:MeasureType, gml:MeasureListType, gml:CodeType, gml:CodeOrNilReasonListType, gml:BooleanOrNilReasonListType, gml:IntegerOrNilReasonList.
Of particular interest are elements that are the heads of substitution groups, and one named choice group. These are the primary reasons for the value objects schema, since they may act as variables in the definition of content models, such as Observations, when it is desired to permit alternative value types to occur some of which may have complex content such as arrays, geometry and time objects, and where it is useful not to prescribe the actual value type in advance. The members of the groups include quantities, category classifications, boolean, count, temporal and spatial values, and aggregates of these.
The value objects are defined in a hierarchy. The following relationships are defined:
- Concrete elements gml:Quantity, gml:Category, gml:Count and gml:Boolean are substitutable for the abstract element gml:AbstractScalarValue.
- Concrete elements gml:QuantityList, gml:CategoryList, gml:CountList and gml:BooleanList are substitutable for the abstract element gml:AbstractScalarValueList.
- Concrete element gml:ValueArray is substitutable for the concrete element gml:CompositeValue.
- Abstract elements gml:AbstractScalarValue and gml:AbstractScalarValueList, and concrete elements gml:CompositeValue, gml:ValueExtent, gml:CategoryExtent, gml:CountExtent and gml:QuantityExtent are substitutable for abstract element gml:AbstractValue.
- Abstract elements gml:AbstractValue, gml:AbstractTimeObject and gml:AbstractGeometry are all in a choice group named gml:Value, which is used for compositing in gml:CompositeValue and gml:ValueExtent.
- Schemas which need values may use the abstract element gml:AbstractValue in a content model in order to permit any of the gml:AbstractScalarValues, gml:AbstractScalarValueLists, gml:CompositeValue or gml:ValueExtent to occur in an instance, or the named group gml:Value to also permit gml:AbstractTimeObjects, gml:AbstractGeometrys.
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See ISO/DIS 19136 20.2.
An implicit description of geometry is one in which the items of the geometry do not explicitly appear in the encoding. Instead, a compact notation records a set of parameters, and a set of objects may be generated using a rule with these parameters. This Clause provides grid geometries that are used in the description of gridded coverages and other applications.
In GML two grid structures are defined, namely gml:Grid and gml:RectifiedGrid.
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See ISO/DIS 19136 13.3.
The spatial-temporal coordinate reference systems schema components are divided into two logical parts. One part defines elements and types for XML encoding of abstract coordinate reference systems definitions. The larger part defines specialized constructs for XML encoding of definitions of the multiple concrete types of spatial-temporal coordinate reference systems.
These schema components encode the Coordinate Reference System packages of the UML Models of ISO 19111 Clause 8 and ISO/DIS 19136 D.3.10, with the exception of the abstract "SC_CRS" class.
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See ISO/DIS 19136 13.4.
The coordinate systems schema components can be divded into three logical parts, which define elements and types for XML encoding of the definitions of:
- Coordinate system axes
- Abstract coordinate system
- Multiple concrete types of spatial-temporal coordinate systems
These schema components encode the Coordinate System packages of the UML Models of ISO 19111 Clause 9 and ISO/DIS 19136 D.3.10.
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See ISO/DIS 19136 13.2.
The reference systems schema components have two logical parts, which define elements and types for XML encoding of the definitions of:
- Identified Object, inherited by the ten types of GML objects used for coordinate reference systems and coordinate operations
- High-level part of the definitions of coordinate reference systems
This schema encodes the Identified Object and Reference System packages of the UML Model for ISO 19111.
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See ISO/DIS 19136 13.5
The datums schema components can be divided into three logical parts, which define elements and types for XML encoding of the definitions of:
- Abstract datum
- Geodetic datums, including ellipsoid and prime meridian
- Multiple other concrete types of spatial or temporal datums
These schema components encode the Datum packages of the UML Models of ISO 19111 Clause 10 and ISO/DIS 19136 D.3.10.
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See ISO/DIS 19136 13.6.
The spatial or temporal coordinate operations schema components can be divided into five logical parts, which define elements and types for XML encoding of the definitions of:
- Multiple abstract coordinate operations
- Multiple concrete types of coordinate operations, including Transformations and Conversions
- Abstract and concrete parameter values and groups
- Operation methods
- Abstract and concrete operation parameters and groups
These schema component encodes the Coordinate Operation package of the UML Model for ISO 19111 Clause 11.
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See ISO/DIS 19136 Clause 19.
A GML observation models the act of observing, often with a camera, a person or some form of instrument. An observation feature describes the "metadata" associated with an information capture event, together with a value for the result of the observation. This covers a broad range of cases, from a tourist photo (not the photo but the act of taking the photo), to images acquired by space borne sensors or the measurement of a temperature 5 meters below the surfaces of a lake.
The basic structures introduced in this schema are intended to serve as the foundation for more comprehensive schemas for scientific, technical and engineering measurement schemas.
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See ISO/DIS 19136 15.5.
A value in the time domain is measured relative to a temporal reference system. Common types of reference systems include calendars, ordinal temporal reference systems, and temporal coordinate systems (time elapsed since some epoch). The primary temporal reference system for use with geographic information is the Gregorian Calendar and 24 hour local or Coordinated Universal Time (UTC), but special applications may entail the use of alternative reference systems. The Julian day numbering system is a temporal coordinate system that has an origin earlier than any known calendar, at noon on 1 January 4713 BC in the Julian proleptic calendar, and is useful in transformations between dates in different calendars.
In GML seven concrete elements are used to describe temporal reference systems: gml:TimeReferenceSystem, gml:TimeCoordinateSystem, gml:TimeCalendar, gml:TimeCalendarEra, gml:TimeClock, gml:TimeOrdinalReferenceSystem, and gml:TimeOrdinalEra.
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See ISO/DIS 19136 15.3.
Temporal topology is described in terms of time complexes, nodes, and edges, and the connectivity between these. Temporal topology does not directly provide information about temporal position. It is used in the case of describing a lineage or a history (e.g. a family tree expressing evolution of species, an ecological cycle, a lineage of lands or buildings, or a history of separation and merger of administrative boundaries). The following Subclauses specifies the temporal topology as temporal characteristics of features in compliance with ISO 19108.
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All global schema components that are part of the GML schema, but were deprecated. See Annex I.
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Application Data
gml.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:gml:3.2.1.
dynamicFeature.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:dynamicFeature:3.2.1.
feature.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:feature:3.2.1.
geometryAggregates.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:geometryAggregates:3.2.1.
geometryPrimitives.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:geometryPrimitives:3.2.1.
geometryBasic2d.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:geometryBasic2d:3.2.1.
geometryBasic0d1d.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:geometryBasic0d1d:3.2.1.
measures.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:measures:3.2.1.
units.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:units:3.2.1.
dictionary.xsd
More information at: urn:opengis:specification:gml:schema-xsd:dictionary:v3.2.1.
gmlBase.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:gmlBase:3.2.1.
basicTypes.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:basicTypes:3.2.1.
temporal.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:temporal:3.2.1.
direction.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:direction:3.2.1.
topology.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:topology:3.2.1.
geometryComplexes.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:geometryComplexes:3.2.1.
coverage.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:coverage:3.2.1.
valueObjects.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:valueObjects:3.2.1.
grids.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:grids:3.2.1.
coordinateReferenceSystems.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:coordinateReferenceSystems:3.2.1.
coordinateSystems.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:coordinateSystems:3.2.1.
referenceSystems.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:referenceSystems:3.2.1.
datums.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:datums:3.2.1.
coordinateOperations.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:coordinateOperations:3.2.1.
observation.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:observation:3.2.1.
temporalReferenceSystems.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:temporalReferenceSystems:3.2.1.
temporalTopology.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:temporalTopology:3.2.1.
deprecatedTypes.xsd
More information at: urn:x-ogc:specification:gml:schema-xsd:deprecatedTypes:3.2.1.
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
gml:AbstractCRS specifies a coordinate reference system which is usually single but may be compound. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
A continuous coverage as defined in ISO 19123 is a coverage that can return different values for the same feature attribute at different direct positions within a single spatiotemporal object in its spatiotemporal domain. The base type for continuous coverages is AbstractContinuousCoverageType.
The coverageFunction element describes the mapping function.
The abstract element gml:AbstractContinuousCoverage serves as the head of a substitution group which may contain any continuous coverage whose type is derived from gml:AbstractContinuousCoverageType.
gml:AbstractCoordinateOperation is a mathematical operation on coordinates that transforms or converts coordinates to another coordinate reference system. Many but not all coordinate operations (from CRS A to CRS B) also uniquely define the inverse operation (from CRS B to CRS A). In some cases, the operation method algorithm for the inverse operation is the same as for the forward algorithm, but the signs of some operation parameter values shall be reversed. In other cases, different algorithms are required for the forward and inverse operations, but the same operation parameter values are used. If (some) entirely different parameter values are needed, a different coordinate operation shall be defined.
The optional coordinateOperationAccuracy property elements provide estimates of the impact of this coordinate operation on point position accuracy.
gml:AbstractCoordinateSystem is a coordinate system (CS) is the non-repeating sequence of coordinate system axes that spans a given coordinate space. A CS is derived from a set of mathematical rules for specifying how coordinates in a given space are to be assigned to points. The coordinate values in a coordinate tuple shall be recorded in the order in which the coordinate system axes associations are recorded. This abstract complex type shall not be used, extended, or restricted, in an Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
This element serves as the head of a substitution group which may contain any coverage whose type is derived from gml:AbstractCoverageType. It may act as a variable in the definition of content models where it is required to permit any coverage to be valid.
A curve segment defines a homogeneous segment of a curve.
The attributes numDerivativesAtStart, numDerivativesAtEnd and numDerivativesInterior specify the type of continuity as specified in ISO 19107:2003, 6.4.9.3.
The AbstractCurveSegment element is the abstract head of the substituition group for all curve segment elements, i.e. continuous segments of the same interpolation mechanism.
All curve segments shall have an attribute interpolation with type gml:CurveInterpolationType specifying the curve interpolation mechanism used for this segment. This mechanism uses the control points and control parameters to determine the position of this curve segment.
A gml:AbstractDatum specifies the relationship of a coordinate system to the earth, thus creating a coordinate reference system. A datum uses a parameter or set of parameters that determine the location of the origin of the coordinate reference system. Each datum subtype may be associated with only specific types of coordinate systems. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
A discrete coverage consists of a domain set, range set and optionally a coverage function. The domain set consists of either spatial or temporal geometry objects, finite in number. The range set is comprised of a finite number of attribute values each of which is associated to every direct position within any single spatiotemporal object in the domain. In other words, the range values are constant on each spatiotemporal object in the domain. This coverage function maps each element from the coverage domain to an element in its range. The coverageFunction element describes the mapping function.
This element serves as the head of a substitution group which may contain any discrete coverage whose type is derived from gml:DiscreteCoverageType.
This abstract element serves as the head of a substitution group which may contain any elements whose content model is derived from gml:AbstractFeatureType. This may be used as a variable in the construction of content models.
gml:AbstractFeature may be thought of as "anything that is a GML feature" and may be used to define variables or templates in which the value of a GML property is "any feature". This occurs in particular in a GML feature collection where the feature member properties contain one or multiple copies of gml:AbstractFeature respectively.
The abstract element gml:AbstractGML is "any GML object having identity". It acts as the head of an XML Schema substitution group, which may include any element which is a GML feature, or other object, with identity. This is used as a variable in content models in GML core and application schemas. It is effectively an abstract superclass for all GML objects.
gm:AbstractGeneralConversion is an abstract operation on coordinates that does not include any change of datum. The best-known example of a coordinate conversion is a map projection. The parameters describing coordinate conversions are defined rather than empirically derived. Note that some conversions have no parameters. The operationVersion, sourceCRS, and targetCRS elements are omitted in a coordinate conversion.
This abstract complex type is expected to be extended for well-known operation methods with many Conversion instances, in GML Application Schemas that define operation-method-specialized element names and contents. This conversion uses an operation method, usually with associated parameter values. However, operation methods and parameter values are directly associated with concrete subtypes, not with this abstract type. All concrete types derived from this type shall extend this type to include a "usesMethod" element that references the "OperationMethod" element. Similarly, all concrete types derived from this type shall extend this type to include zero or more elements each named "uses...Value" that each use the type of an element substitutable for the "AbstractGeneralParameterValue" element.
gml:AbstractGeneralDerivedCRS is a coordinate reference system that is defined by its coordinate conversion from another coordinate reference system. This abstract complex type shall not be used, extended, or restricted, in a GML Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
gml:AbstractGeneralParameterValue is an abstract parameter value or group of parameter values.
This abstract complexType is expected to be extended and restricted for well-known operation methods with many instances, in Application Schemas that define operation-method-specialized element names and contents. Specific parameter value elements are directly contained in concrete subtypes, not in this abstract type. All concrete types derived from this type shall extend this type to include one "...Value" element with an appropriate type, which should be one of the element types allowed in the ParameterValueType. In addition, all derived concrete types shall extend this type to include a "operationParameter" property element that references one element substitutable for the "OperationParameter" object element.
gml:AbstractGeneralTransformation is an abstract operation on coordinates that usually includes a change of Datum. The parameters of a coordinate transformation are empirically derived from data containing the coordinates of a series of points in both coordinate reference systems. This computational process is usually "over-determined", allowing derivation of error (or accuracy) estimates for the transformation. Also, the stochastic nature of the parameters may result in multiple (different)
versions of the same coordinate transformation. The operationVersion, sourceCRS, and targetCRS proeprty elements are mandatory in a coordinate transformation.
This abstract complex type is expected to be extended for well-known operation methods with many Transformation instances, in Application Schemas that define operation-method-specialized value element names and contents. This transformation uses an operation method with associated parameter values. However, operation methods and parameter values are directly associated with concrete subtypes, not with this abstract type. All concrete types derived from this type shall extend this type to include a "usesMethod" element that references one "OperationMethod" element. Similarly, all concrete types derived from this type shall extend this type to include one or more elements each named "uses...Value" that each use the type of an element substitutable for the "AbstractGeneralParameterValue" element.
The AbstractGeometry element is the abstract head of the substitution group for all geometry elements of GML. This includes pre-defined and user-defined geometry elements. Any geometry element shall be a direct or indirect extension/restriction of AbstractGeometryType and shall be directly or indirectly in the substitution group of AbstractGeometry.
if provided, rows gives the number of rows, columns the number of columns in the parameter grid. The parameter grid is represented by an instance of the gml:PointGrid group.
The element provides a substitution group head for the surface patches based on a grid. All derived subtypes shall conform to the constraints specified in ISO 19107:2003, 6.4.41.
This element has no type defined, and is therefore implicitly (according to the rules of W3C XML Schema) an XML Schema anyType. It is used as the head of an XML Schema substitution group which unifies complex content and certain simple content elements used for datatypes in GML, including the gml:AbstractGML substitution group.
The element provides a substitution group head for the surface patches based on parametric curves. All properties are specified in the derived subtypes. All derived subtypes shall conform to the constraints specified in ISO 19107:2003, 6.4.40.
If provided, the aggregationType attribute shall have the value "set".
An abstraction of a ring to support surface boundaries of different complexity.
The AbstractRing element is the abstract head of the substituition group for all closed boundaries of a surface patch.
gml:AbstractScalarValue is an abstract element which acts as the head of a substitution group which contains gml:Boolean, gml:Category, gml:Count and gml:Quantity, and (transitively) the elements in their substitution groups.
gml:AbstractScalarValueList is an abstract element which acts as the head of a substitution group which contains gml:BooleanList, gml:CategoryList, gml:CountList and gml:QuantityList, and (transitively) the elements in their substitution groups.
A surface patch defines a homogenuous portion of a surface.
The AbstractSurfacePatch element is the abstract head of the substituition group for all surface patch elements describing a continuous portion of a surface.
All surface patches shall have an attribute interpolation (declared in the types derived from gml:AbstractSurfacePatchType) specifying the interpolation mechanism used for the patch using gml:SurfaceInterpolationType.
gml:TimeGeometricPrimitive acts as the head of a substitution group for geometric temporal primitives.
A temporal geometry shall be associated with a temporal reference system through the frame attribute that provides a URI reference that identifies a description of the reference system. Following ISO 19108, the Gregorian calendar with UTC is the default reference system, but others may also be used. The GPS calendar is an alternative reference systems in common use.
The two geometric primitives in the temporal dimension are the instant and the period. GML components are defined to support these as follows.
To describe an event — an action that occurs at an instant or over an interval of time — GML provides the gml:AbtractTimeSlice element. A timeslice encapsulates the time-varying properties of a dynamic feature -- it shall be extended to represent a time stamped projection of a specific feature. The gml:dataSource property describes how the temporal data was acquired.
A gml:AbstractTimeSlice instance is a GML object that encapsulates updates of the dynamic—or volatile—properties that reflect some change event; it thus includes only those feature properties that have actually changed due to some process.
gml:AbstractTimeSlice basically provides a facility for attribute-level time stamping, in contrast to the object-level time stamping of dynamic feature instances.
The time slice can thus be viewed as event or process-oriented, whereas a snapshot is more state or structure-oriented. A timeslice has richer causality, whereas a snapshot merely portrays the status of the whole.
gml:TimeTopologyPrimitive acts as the head of a substitution group for topological temporal primitives.
Temporal topology primitives shall imply the ordering information between features or feature properties. The temporal connection of features can be examined if they have temporal topology primitives as values of their properties. Usually, an instantaneous feature associates with a time node, and a static feature associates with a time edge. A feature with both modes associates with the temporal topology primitive: a supertype of time nodes and time edges.
A topological primitive is always connected to one or more other topological primitives, and is, therefore, always a member of a topological complex. In a GML instance, this will often be indicated by the primitives being described by elements that are descendents of an element describing a complex. However, in order to support the case where a temporal topological primitive is described in another context, the optional complex property is provided, which carries a reference to the parent temporal topological complex.
gml:AbstractTopoPrimitive acts as the base type for all topological primitives. Topology primitives are the atomic (smallest possible) units of a topology complex.
Each topology primitive may contain references to other topology primitives of codimension 2 or more (gml:isolated). Conversely, nodes may have faces as containers and nodes and edges may have solids as containers (gml:container).
gml:AbstractValue is an abstract element which acts as the head of a substitution group which contains gml:AbstractScalarValue, gml:AbstractScalarValueList, gml:CompositeValue and gml:ValueExtent, and (transitively) the elements in their substitution groups.
These elements may be used in an application schema as variables, so that in an XML instance document any member of its substitution group may occur.
gml:AffineCS is a two- or three-dimensional coordinate system with straight axes that are not necessarily orthogonal. An AffineCS shall have two or three gml:axis property elements; the number of property elements shall equal the dimension of the CS.
An Arc is an arc string with only one arc unit, i.e. three control points including the start and end point. As arc is an arc string consisting of a single arc, the attribute "numArc" is fixed to "1".
An ArcByBulge is an arc string with only one arc unit, i.e. two control points, one bulge and one normal vector.
As arc is an arc string consisting of a single arc, the attribute "numArc" is fixed to "1".
This variant of the arc requires that the points on the arc shall be computed instead of storing the coordinates directly. The single control point is the center point of the arc plus the radius and the bearing at start and end. This representation can be used only in 2D.
The element radius specifies the radius of the arc.
The element startAngle specifies the bearing of the arc at the start.
The element endAngle specifies the bearing of the arc at the end.
The interpolation is fixed as "circularArcCenterPointWithRadius".
Since this type describes always a single arc, the attribute "numArc" is fixed to "1".
The content model follows the general pattern for the encoding of curve segments.
An ArcString is a curve segment that uses three-point circular arc interpolation ("circularArc3Points"). The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be 2 * numArc + 1.
The content model follows the general pattern for the encoding of curve segments.
This variant of the arc computes the mid points of the arcs instead of storing the coordinates directly. The control point sequence consists of the start and end points of each arc plus the bulge (see ISO 19107:2003, 6.4.17.2). The normal is a vector normal (perpendicular) to the chord of the arc (see ISO 19107:2003, 6.4.17.4).
The interpolation is fixed as "circularArc2PointWithBulge".
The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be numArc + 1.
The content model follows the general pattern for the encoding of curve segments.
A B-Spline is a piecewise parametric polynomial or rational curve described in terms of control points and basis functions as specified in ISO 19107:2003, 6.4.30. Therefore, interpolation may be either "polynomialSpline" or "rationalSpline" depending on the interpolation type; default is "polynomialSpline".
degree shall be the degree of the polynomial used for interpolation in this spline.
knot shall be the sequence of distinct knots used to define the spline basis functions (see ISO 19107:2003, 6.4.26.2).
The attribute isPolynomial shall be set to "true" if this is a polynomial spline (see ISO 19107:2003, 6.4.30.5).
The attribute knotType shall provide the type of knot distribution used in defining this spline (see ISO 19107:2003, 6.4.30.4).
The content model follows the general pattern for the encoding of curve segments.
A base unit is a unit of measure that cannot be derived by combination of other base units within a particular system of units. For example, in the SI system of units, the base units are metre, kilogram, second, Ampere, Kelvin, mole, and candela, for the physical quantity types length, mass, time interval, electric current, thermodynamic temperature, amount of substance and luminous intensity, respectively.
gml:BaseUnit extends generic gml:UnitDefinition with the property gml:unitsSystem, which carries a reference to the units system to which this base unit is asserted to belong.
Bezier curves are polynomial splines that use Bezier or Bernstein polynomials for interpolation purposes. It is a special case of the B-Spline curve with two knots.
degree shall be the degree of the polynomial used for interpolation in this spline.
knot shall be the sequence of distinct knots used to define the spline basis functions.
interpolation is fixed as "polynomialSpline".
isPolynomial is fixed as "true".
knotType is not relevant for Bezier curve segments.
gml:CartesianCS is a 1-, 2-, or 3-dimensional coordinate system. In the 1-dimensional case, it contains a single straight coordinate axis. In the 2- and 3-dimensional cases gives the position of points relative to orthogonal straight axes. In the multi-dimensional case, all axes shall have the same length unit of measure. A CartesianCS shall have one, two, or three gml:axis property elements.
A Circle is an arc whose ends coincide to form a simple closed loop. The three control points shall be distinct non-co-linear points for the circle to be unambiguously defined. The arc is simply extended past the third control point until the first control point is encountered.
A gml:CircleByCenterPoint is an gml:ArcByCenterPoint with identical start and end angle to form a full circle. Again, this representation can be used only in 2D.
A clothoid, or Cornu's spiral, is plane curve whose curvature is a fixed function of its length.
refLocation, startParameter, endParameter and scaleFactor have the same meaning as specified in ISO 19107:2003, 6.4.22.
interpolation is fixed as "clothoid".
The content model follows the general pattern for the encoding of curve segments.
A gml:CompositeCurve is represented by a sequence of (orientable) curves such that each curve in the sequence terminates at the start point of the subsequent curve in the list.
curveMember references or contains inline one curve in the composite curve.
The curves are contiguous, the collection of curves is ordered. Therefore, if provided, the aggregationType attribute shall have the value "sequence".
gml:CompositeSolid implements ISO 19107 GM_CompositeSolid (see ISO 19107:2003, 6.6.7) as specified in D.2.3.6.
A gml:CompositeSolid is represented by a set of orientable surfaces. It is a geometry type with all the geometric properties of a (primitive) solid. Essentially, a composite solid is a collection of solids that join in pairs on common boundary surfaces and which, when considered as a whole, form a single solid.
solidMember references or contains one solid in the composite solid. The solids are contiguous.
A gml:CompositeSurface is represented by a set of orientable surfaces. It is geometry type with all the geometric properties of a (primitive) surface. Essentially, a composite surface is a collection of surfaces that join in pairs on common boundary curves and which, when considered as a whole, form a single surface.
surfaceMember references or contains inline one surface in the composite surface.
The surfaces are contiguous.
gml:CompositeValue is an aggregate value built from other values . It contains zero or an arbitrary number of gml:valueComponent elements, and zero or one gml:valueComponents property elements. It may be used for strongly coupled aggregates (vectors, tensors) or for arbitrary collections of values.
gml:CompundCRS is a coordinate reference system describing the position of points through two or more independent coordinate reference systems. It is associated with a non-repeating sequence of two or more instances of SingleCRS.
Conventional units that are neither base units nor defined by direct combination of base units are used in many application domains. For example electronVolt for energy, feet and nautical miles for length. In most cases there is a known, usually linear, conversion to a preferred unit which is either a base unit or derived by direct combination of base units.
The gml:ConventionalUnit extends gml:UnitDefinition with a property that describes a conversion to a preferred unit for this physical quantity. When the conversion is exact, the element gml:conversionToPreferredUnit should be used, or when the conversion is not exact the element gml:roughConversionToPreferredUnit is available. Both of these elements have the same content model. The gml:derivationUnitTerm property defined above is included to allow a user to optionally record how this unit may be derived from other ("more primitive") units.
gml:Conversion is a concrete operation on coordinates that does not include any change of Datum. The best-known example of a coordinate conversion is a map projection. The parameters describing coordinate conversions are defined rather than empirically derived. Note that some conversions have no parameters.
This concrete complex type can be used without using a GML Application Schema that defines operation-method-specialized element names and contents, especially for methods with only one Conversion instance.
The usesValue property elements are an unordered list of composition associations to the set of parameter values used by this conversion operation.
gml:CoverageMappingRule provides a formal or informal description of the coverage function.
The mapping rule may be defined as an in-line string (gml:ruleDefinition) or via a remote reference through xlink:href (gml:ruleReference).
If no rule name is specified, the default is 'Linear' with respect to members of the domain in document order.
The number of control points shall be at least three.
vectorAtStart is the unit tangent vector at the start point of the spline. vectorAtEnd is the unit tangent vector at the end point of the spline. Only the direction of the vectors shall be used to determine the shape of the cubic spline, not their length.
interpolation is fixed as "cubicSpline".
degree shall be the degree of the polynomial used for the interpolation in this spline. Therefore the degree for a cubic spline is fixed to "3".
The content model follows the general pattern for the encoding of curve segments.
A curve is a 1-dimensional primitive. Curves are continuous, connected, and have a measurable length in terms of the coordinate system.
A curve is composed of one or more curve segments. Each curve segment within a curve may be defined using a different interpolation method. The curve segments are connected to one another, with the end point of each segment except the last being the start point of the next segment in the segment list.
The orientation of the curve is positive.
The element segments encapsulates the segments of the curve.
gml:CylindricalCS is a three-dimensional coordinate system consisting of a polar coordinate system extended by a straight coordinate axis perpendicular to the plane spanned by the polar coordinate system. A CylindricalCS shall have three gml:axis property elements.
gml:DataBlock describes the Range as a block of text encoded values similar to a Common Separated Value (CSV) representation.
The range set parameterization is described by the property gml:rangeParameters.
The basic gml:Definition element specifies a definition, which can be included in or referenced by a dictionary.
The content model for a generic definition is a derivation from gml:AbstractGMLType.
The gml:description property element shall hold the definition if this can be captured in a simple text string, or the gml:descriptionReference property element may carry a link to a description elsewhere.
The gml:identifier element shall provide one identifier identifying this definition. The identifier shall be unique within the dictionaries using this definition.
The gml:name elements shall provide zero or more terms and synonyms for which this is the definition.
The gml:remarks element shall be used to hold additional textual information that is not conceptually part of the definition but is useful in understanding the definition.
gml:DerivedCRS is a single coordinate reference system that is defined by its coordinate conversion from another single coordinate reference system known as the base CRS. The base CRS can be a projected coordinate reference system, if this DerivedCRS is used for a georectified grid coverage as described in ISO 19123, Clause 8.
Derived units are defined by combination of other units. Derived units are used for quantities other than those corresponding to the base units, such as hertz (s-1) for frequency, Newton (kg.m/s2) for force. Derived units based directly on base units are usually preferred for quantities other than the fundamental quantities within a system. If a derived unit is not the preferred unit, the gml:ConventionalUnit element should be used instead.
The gml:DerivedUnit extends gml:UnitDefinition with the property gml:derivationUnitTerms.
Sets of definitions may be collected into dictionaries or collections.
A gml:Dictionary is a non-abstract collection of definitions.
The gml:Dictionary content model adds a list of gml:dictionaryEntry properties that contain or reference gml:Definition objects. A database handle (gml:id attribute) is required, in order that this collection may be referred to. The standard gml:identifier, gml:description, gml:descriptionReference and gml:name properties are available to reference or contain more information about this dictionary. The gml:description and gml:descriptionReference property elements may be used for a description of this dictionary. The derived gml:name element may be used for the name(s) of this dictionary. for remote definiton references gml:dictionaryEntry shall be used. If a Definition object contained within a Dictionary uses the descriptionReference property to refer to a remote definition, then this enables the inclusion of a remote definition in a local dictionary, giving a handle and identifier in the context of the local dictionary.