02-17-2008, 02:25 PM
The type of GPS that surveyors use is called differential GPS. The $100 handheld kind is regular GPS. If I understand correctly, given a single shot measured from space you are lucky to get within a few feet. However differential GPS measures two points simultaneously. While they may both be off by 5 feet, they are off by the same 5 feet in the same direction, so if you know the position of one point you can determine the position of the other point within fractions of an inch. The key is you have to start with at least one well known point.
My neighbor and I put up a fence between our properties using a regular old handheld GPS unit. We both knew it would not be super accurate and we could tell as the location would drift back and forth by a few feet as you were standing there watching the screen. However we could never have gotten even that close through the trackless jungle without it. If we ever clear the property line to achieve line of sight from pin to pin we will see that the fence wanders quite a bit.
My neighbor and I put up a fence between our properties using a regular old handheld GPS unit. We both knew it would not be super accurate and we could tell as the location would drift back and forth by a few feet as you were standing there watching the screen. However we could never have gotten even that close through the trackless jungle without it. If we ever clear the property line to achieve line of sight from pin to pin we will see that the fence wanders quite a bit.