Ahh, sorry - misinterpreted what you meant. I see this behaviour almost all the time, I just use the mid point.
cheers On Jan 23, 2008 5:44 AM, Harald Kirsch <[EMAIL PROTECTED]> wrote: > > > 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 > -- Franc
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