AGPS - protocol specs?

Bartlomiej Zdanowski AutoGuard Ltd. b.zdanowski at
Fri Mar 9 09:58:03 CET 2007


Nils Faerber napisał(a):
>> There is all sorts of wacky stuff - for example, peer-peer DGPS that can
>> be done, where all stationary neos on charge with a GPS signal and a
>> free internet connection contribute to a global ionospheric model.
>> Then any Neo can connect to this model, download 200 bytes or so, and
>> get +-0.3m (or better) position for a short while.
> Exactly.
> Also relative positioning can be made much more precise using the raw
> data (AFAIK in the range of cm not m).
I asked my colleagues who are GPS devices specialists and they said that 
this is all wrong. Military devices can do magic but civil not. They 
said that with civil GPS receiver you can get accuracy up to about 5 - 
10 meters. For such precision it is required to be seen at least 8 
satellites, a clear sky and good magnetic and ionosphere  conditions 
(also solar magnetic field's change is important).
To get *any* GPS reading device must see 3 satellites but you cannot be 
sure the position. It can vary even up to hundreds of meters!
Of course you can get very accurate reading but device must see many 
satellites and stand up still for many hours! Then the mean value is 
computed and can be assumed that GPS position reading is accurate to 

You cannot depend on GPS reading to count quite accurate velocity, 
acceleration and accurate position. Sorry.

*Bartlomiej Zdanowski*
Product Research Department
AutoGuard & Insurance Ltd.

Omulewska 27 street
04-128 Warsaw
phone +48 22 611 69 23 <>
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