Where 3D rendering engines can work vectorially, projecting all faces in the camera plane in increasing order of distance to the sensor, in radar this approach is not possible. The projection plane of the image is not the plane of the sensor, and therefore the calculation of the faces that are hidden must be done separately.
If we consider a flat earth model, we can define the following two reference frames:
The terrestrial reference frame. This is the classical cartographic reference frame (x,y,z), where x is traditionally oriented in the East-West direction, y in the North-South direction, and z oriented upwards, normal to the terrestrial plane assumed locally flat and horizontal.