Why bother with GPS or other "absolute" coordinate systems? Once the rocket's in close, all that matters is relative position and orientation of the rocket with

Why bother with GPS or other "absolute" coordinate systems? Once the rocket's in close, all that matters is relative position and orientation of the rocket with respect to the landing apparatus. Eg, if you had many sensors in known locations on the rocket and many sensors in known locations on the landing apparatus, and you could measure relative positions between all pairs of these sensors, you could get extremely precise relative position/orientation information without beaming information to satellites or whatever.