[OSM-newbies] Consistently off tracks on second or third tracking

[Franc Carter]

Out of curiosity, how do you know it's off, whenever I think about this sort
of thing
I have a really hard time working out what might be a good 'source of
truth'.

cheers

On Jan 21, 2008 7:48 AM, Nick Black <nickblack1 at gmail.com> wrote:

> On Jan 20, 2008 6:36 PM, Lauri Hahne <lauri.hahne at gmail.com> wrote:
> > On 20/01/2008, Lars Aronsson <lars at aronsson.se> 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
> > newbies at openstreetmap.org
> > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies
> >
>
>
>
> --
> Nick Black
> --------------------------------
> http://www.blacksworld.net
>
> _______________________________________________
> newbies mailing list
> newbies at openstreetmap.org
> http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/newbies
>



-- 
Franc
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/newbies/attachments/20080121/358e5b1a/attachment.html>