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.
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.
Source
<element name="SphericalCS" type="gml:SphericalCSType" substitutionGroup="gml:AbstractCoordinateSystem"><annotation><documentation>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.</documentation></annotation></element>