I've seen sub-centimeter accuracy while using this device. Although it's a little pricey (approx 30k if i remember), it's still a civilian unit.
Doesn't matter.. you aren't going to get better than 10m accuracy without DGPS and 1m with it. Surveys have to be right to centimetres - no GPS can do that (possibly some of the military stuff, but I'd be surprised if even they were that accurate).
You don't need military GPS to be that accurate, it can be done with differential phase GPS. See: here. By using a fixed base station at a location with known coordinates, one can expect to see accuracies in the 1 to 2 cm range as long as the receiver is within 10's of km from the base station. There are several manufacturers who make gear that can achieve this level of accuracy, see Leica, Magellan, and Sokkia. I've been using Leica gear at work mostly, and have see ~1cm accuracy under good conditions pretty consistently. A lot of legal surveying in remote areas is done exclusively with GPS, especially in the northern parts of B.C and Alberta. I've done legal surveys with GPS in the Vancouver area, but getting high accuracy in urban areas is more difficult because of multi-path noise and qoor signal quality from obstructions such as buildings. Also people in the city get mad when you cut down trees to get better reception
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