Quote: Originally Posted by gommino
I doubt it since the GPS satellites are geo-stationary.
Rob.
This is not true. All the GPS sats are on elliptical orbits. The orbits are somwhat predictable, but the sats never follow the exact path they are supposed to. There are radar stations throughout the world that track the sats exact movement, and every 12 hours upload the azimuth (the specific mathematical equation describing the satellites path) to each satellite. The radar stations use the information gathered over the past 12 hours to "guess" what the azimuth will be for the next 12 hours.
When your GPS receiver talks to a satellite, the sat has no idea where it is, per se. It just tells your receiver what it's azimuth is, and what "time" it is for the sat (in other words, how far along the path of the azimuth the sat is) and the receiver figures out where the sat is.
Then using, time shift, the receiver figures out how far it is from the sat. Do that for 3 sats, and you have your 2D location.
My guess, is the above is a PDA program (There are many out there) that will output the sats (and their info) a given receiver sees. This is mainly used for testing new receivers - but it's pretty neat to watch the sats "rise" and "set."
Linear Mode
