On March 10, 2008 09:01:24 am Curtis Olson wrote: > I'm not a gps guy, but I think differential gps systems work based on the > phase of the signal and the stations select a common set of satellites for > their solution. We actually have a person a the UofMN working on a project > where the two ends can be mobile and the system computes the relative > distance between the two mobile station ... so you could plunk one end down > at the end of your temporary runway for doing virtual ILS/precision > landings. But that still doesn't fully resolve that the real world ground > elevation may not match exactly the elevation in FlightGear so there will > always be some kind of discrepancy when rendering real flight data in a > simulator ... especially when taxiing or touching down. > > Regards, > > Curt.
Hello Curt, Now that you've mentioned "common set of satellites", you have reminded me that corrections are made to the pseudorange observations, not the calculated position of the receiver as I have stated incorrectly earlier. Pseudorange is the distance between the receiver and the satellite measured by the receiver. Regarding the phase: technically, all GPS positioning deals with phase. But you shouldn't have to deal with it, and it is most likely not worth the effort to deal with in this project of yours anyway. You are not trying to implement a GPS receiver here. What you want to do is to just post process the observations and screen out the jumps. Phase could come into play if you are correcting for atmospheric and ionospheric refraction. In your case however, if your receivers are within 500 km range, the errors introduced to your baseline by refraction would be neglegable. For your last problem regarding Flightgear scenery: suppose you have used two receivers and recorded the relative movement of the plane with respect to the ground station. In FG, you could do the reverse by moving the model with respect to a reference point on the terrain. As long as your local terrain is a large flat area, the resulting visualization should not have too many instances of model submerging into the ground. :) Ampere ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
