On Jan 20, 2008 6:36 PM, Lauri Hahne <[EMAIL PROTECTED]> wrote: > On 20/01/2008, Lars Aronsson <[EMAIL PROTECTED]> wrote: > > Harald Kirsch wrote: > > > > > Now, if the GPS would produce a Gaussian error, I would expect a > > > track to zigzag left and right from an older track, but > > > obviously this is not the case. > > > > The error is random (Gaussian or not), but not in every sample. > > Satellites drift slightly out off course, and are corrected into > > the right orbit once in a while. You can get exactly the correct > > position relative to the satellite, but the satellite can be 7 > > metres out of its planned orbit. So your position might also be 7 > > metres off. If you could know how much off each satellite is at > > each moment, you might be able to calculate your correct position > > with much higher accuracy. There are several schemes for this, > > some are military and secret, one is called "WAAS", another is > > called EGNOS. You can learn more by googling these terms. > > > > Actually all GPS satellites broadcast correction parametres for their > orbits. So that isn't a problem.
Yes it is - errors occur because of misjudged orbital paths. The signal broadcast by Navastar contains an estimate of the orbit, not the exact orbit. > > WAAS and EGNOS (together known as SBAS) broadcasts information about > ionospheric errors which amount to most error there is. This > information is collected by ground stations who measure their position > and compare that to their known location. > > A quick googling found the following page > http://www.kowoma.de/en/gps/errors.htm It isn't a very accurate paper > but it gives you the basics. > > > -- > Lauri Hahne > > > _______________________________________________ > newbies mailing list > [email protected] > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies > -- Nick Black -------------------------------- http://www.blacksworld.net _______________________________________________ newbies mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies
