I used a Garmin Nuvi to get to the Lakeland Rifle and Pistol Club gun show in Lakeland, Florida this weekend. Several times it though I was on the next street over from where I really was. Distance errors of as much as yards. Not good enough for survey work!
Better units with greater accuracy are available but as with everything else, precision costs. High precision costs highly.
I don't think that people should put all their measurement eggs in one satellite-based basket, either. To me, GPS based surveys
should only be a guideline, not an absolute reference. GPS drifts, but the US Geodetic Survey markers generally don't. And
they don't rely on millions of dollar's worth of technology to work.
CJ