gml:UserDefinedCS is a two- or three-dimensional coordinate system thatconsists of any combination of coordinate axes not covered by any other coordinate systemtype. A UserDefinedCS shall have two or three gml:axis property elements; the number ofproperty elements shall equal the dimension of the CS.
Database handle for the object. It is of XML type ID, so is constrained to beunique in the XML document within which it occurs. An external identifier for the object inthe form of a URI may be constructed using standard XML and XPointer methods. This is doneby concatenating the URI for the document, a fragment separator, and the value of the idattribute.
Source
<element name="UserDefinedCS" type="gml:UserDefinedCSType" substitutionGroup="gml:AbstractCoordinateSystem"><annotation><documentation>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.</documentation></annotation></element>