Am 20.01.2008 23:03 schrieb Franc Carter: > Out of curiosity, how do you know it's off,
If I ride three times the same street and no two recorded tracks agree with each other, then obviously at least two of them are off. In my original post I was not suggesting that one of them is 'the truth'. HaraldK > cheers > > On Jan 21, 2008 7:48 AM, Nick Black <[EMAIL PROTECTED]> wrote: > >> 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 >> > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > newbies mailing list > [email protected] > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies -- --------------+--------------------------------------------- Harald Kirsch | pifpafpuf bei gmx punkt de _______________________________________________ newbies mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies
