[Lloyd Burns]

The GPS I have takes a minute or two or four to lock in the open, and never if in the vicinity of reflecting surfaces (like large buildings).

GPS dithering was removed several years back, but the resolution of ordinary equipment is metre, not centimetres, Surveyors have equipment that measures the phase of the received carriers, to calculate to millimetres.

A setup that had three transmitting stations in the field corners similar to the VOR stations used for air navigation, which allow the receiver to determine the course to the transmitter in degrees true, would be neat - and if First set them up, everyone could use it, and position would not be a problem. They work like a flashlight rotating round and round at constant speed, casting a horizontal beam as it does. In effect, another light flashes as the beam goes past true north. You start timing when you see the flash, and stop when you see the beam. Three receivers would not be expensive, but the 1 degree phase-shifting antenna for the transmitter might be, as well as having 12 of them at finals.

If you have seen little round buildings wearing white conical witches hats with vertical spikes around the brim, you have seen a VHF Omni Range statoin. We used to see one beside I-5 (in Ohio ?). Use two or three to determine your position. In flying an aircraft, the transmitter locations are on the map, and are thus a known quantity.

Perhaps coloured lights could work. As an added advantage, your heading could be determined. using any one of the three. You'd have to be line of sight to at least two. Wouldn't that be fun programming ?