Comment on Increasing Local GPS Accuracy for a Small Robot by Paul

Motorola in the 80s manufactured the "Mini-Ranger" for ship navigation within harbors. It used microwave (C-band) transponder beacons at fixed locations on shore, and a transceiver on the boat. It measured time of flight to the fixed beacons to compute the ship location. Motorola claimed a precision of a few centimeters. In practice, it could do +/-1 meter at 10 km, and had a range out to 30 km. Mindblowing at the time.

Omega was useless on the harbour scale, even LORAN was too imprecise for harbor and channel nav. Visual aids were often blocked by fog and still were quite imprecise. NavStar was still too immature, and GPS wasn't around yet. For that few-year window in the 80s, the Mini-Ranger enabled precision navigation.

It would be almost trivial to reproduce that now, and down to millimeters. And no satellites required.