information about the reference system identifier and codespace for reference systeme.g. EPSG::4326 Condition: At least one of referenceSystemIdentifier or crs is required full description of the coordinate reference system to which a coordinate set is referenced Condition: At least one of referenceSystemIdentifier or crs is required epoch at which a coordinate set to a dynamic CRS is valid Condition: Reqired if the CRS is dynamic, otherwise should not be given type of reference system identifiede.g. geographic2D defines type of reference system used