"Tom Roberts" <tjroberts137@sbcglobal.net> wrote in message 
news:HpRRg.15897$IA.12921@newssvr11.news.prodigy.com...
| Sorcerer wrote:
| > The underlying premise of differential GPS requires that a GPS receiver, 
| > known as the base station, be set up on a precisely known location. The base 
| > station receiver [...]
|
| You got it backwards. Why don't you LEARN about the subject before writing?

Why don't you LEARN about the subject before writing, fuckin' stupid 
snipping moron?
Androcles.

| Differential GPS involves a TRANSMITTER located at a precisely known 
| ground location. It broadcasts just like a satellite, using an "orbit" 
| with an altitude of a few meters, a period of ~24 hours, etc. Any good 
| GPS receiver within range of its signal can add it into the set of 
| satellites used to determine position. Because of the way a good GPS |
| receiver propagates errors in its computation, the ground transmitter 
| will dominate the computation, yielding a significantly more accurate 
| value than without it.
|
|
| Tom Roberts