Spatial Reference Frames and <Location>
All relationships in the DRM that need locations are specified with the <Location> class or its abstract subclasses, so all the SRM's spatial reference frames are supported for all such relationships.
The requirement that a given <Location> shall be valid in the spatial reference frame it appears in is specified as a constraint. Since the <Environment Root> in our example is 3D celestiodetic, <CD Location 3D>s are used.