R: Need info on AGPS

Marcus Bauer marcus.bauer at gmail.com
Thu Jan 25 17:02:13 CET 2007

On Thu, 2007-01-25 at 16:39 +0100, Andreas Kostyrka wrote:

> Well, it does or not. The question is, does AGPS help with accuracy?

AGPS is a marketing term invented by the mobile industry and their
caterers. The reference docs for the SiRF binary protocol simply calls
these functions "set ephemeris" and "set almanac".

The network can't help the chip at all, execept providing this data so
that the chip can use a satellite in the moment it comes into sight and
doesn't first have to wait 30 seconds while receiving the ephemeris

The accuracy of AGPS and GPS is exactly the same. 

> Just an observation, that my builtin car navigation, which got GPS and
> travel information from the car, sometimes in long parallel running
> streets mistakes the street it is on :(

Then AGPS will do the same mistake.

The way that the 'Global Locate Library' works it is an evil trick to
prevent you from doing this yourself and force you back into the arms of
the mobile operators so that you have to pay for it. I wouldn't be
surprised if the European Comission fines them one day - they have
become quite good in doing so lately.

Nevertheless you don't need the A of AGPS, it is a convenience to get a
quick cold-start positon fix somewhere in the city.

It is just some kind of road toll between you and the free GPS signal
from the sky / ephemeris data from the internet. 


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