Can you clarify what you mean by a fixed reference and a ground-based reference? They sound the same to me, although for the latter I believe you may be talking

Can you clarify what you mean by a fixed reference and a ground-based reference? They sound the same to me, although for the latter I believe you may be talking about a VORTAC or other radio-based ground station, as opposed to pilotage(looking outside and seeing the ground).