AGPS - protocol specs?

Wolfgang S. Rupprecht wolfgang.rupprecht+gnus200703 at
Fri Mar 9 19:28:34 CET 2007

Bartłomiej Zdanowski DRP AC2
<b.zdanowski at> writes:
> I work for company that develops devices for car and person tracking. We
> do the stuff as written above to correct GPS readings.
> A car that is parked in front of our office equipped in GPS receiver
> collects data about it position. Even if is parked in the same place for
> all day, with a clear sky above (a many satellites visible), raw GPS
> readings show that it hangs around all day in range of a few tens of
> meters and sometimes a hundred of meters. And I can assure the we use good
> GPS receivers.

I wonder if you'd do better with a slightly better GPS or better GPS
antenna.  With a good consumer GPS and an unobstructed sky view all
around you shouldn't be averaging a >10 meter error.  Even a 10 year
old, gps designed during the days of "Seleective Availability" did
~2.5 meters in a 24hr test here.  I would expect the modern units to
be even tighter.

In practice when overlaying gps tracklogs with geo-referenced overhead
imagery I regularly see good enough tracking to have a very good guess
as to which lane the car was driving in.  Look at the exit ramp
screenshot (second from the top) to see what I mean.

And yes, I'm going to try to port this mapping program to openmoko.
The real fun starts when everyone you know has one and you can see
where they are on the map in real-time.

Wolfgang S. Rupprecht      

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