Ground reference stations as an additional navigation check

Known-position ground stations provide an alternative reference to a satellite constellation. Civil-engineering equipment is used as the example: dozer blades and excavator buckets can use those stations to maintain the positions required by a plan. Directional antennas and suitable equipment are proposed as a way to apply the principle to military navigation. The proposal assumes an electronic environment permissive enough for the signals to work, so it is not offered as protection against every kind of interference.