I agree with your definition, Bill, but I would be inclined to think that achieving the accuracy necessary for this sort of measurement, using the GPS would qualify as "b....y good"
Well, it does require a lot of patience to get it that good. In fact it requires even more patience than it takes to just get a good reading. You have to keep doing it over and over, because of course the surface of the Earth isn't stable. For the kind of accuracy they need even very small changes in the Earth will affect the distance.
I know that the Earth shifts because one of the last projects I worked on before I retired was to find an automated way to determine true North for the inertial guidance package on the Delta IV Launch Vehicle. There is a standardized way they use on the Delta II which uses a theodolite to make several very precise measurements to determine the value to upload to the guidance system. But it is done the day before the launch, while they can still have people in the area of the vehicle. For some reason they don't want people close to the vehicle just before launch. Something about it being a hazardous location. Anyway they wanted a way to do the measurement in real time just before launch. I came up with several concepts of ways it might be done, but nothing with off-the-shelf equipment, so they attacked it from the other end and settled for the day before measurement.
The thing about this is that the measurement requires several precisely located points in the vicinity of the launch pad and they have to resurvey the site every year to make sure they haven't drifted. Now this was in Florida, which is not very seismically active, but is built on rather soft material that drifts pretty badly. The sites at CERN and OPERA are more stable, but I don't think they are stable enough to maintain their separation for all that long, at least not for the accuracy they need.
Bill Gill
