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

[Lars Aronsson]

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.


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se