Thread: Why does my N900 look for internet connection to use GPS?
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chemist is offline chemist
2010-08-31 , 22:09
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#18
To strip this down and answer some hardware and gps-tech questions.

If it asks for network connection depends on your settings -> location.

Originally Posted by mthmob View Post
The nokia support is wrong in that statement. The n900 contains a real gps antenna.. however its weaker compared to car navigation devices gps antenna..

Therefor it uses what is called a-gps (assisted gps) and accesses internet to get information on where current gps salitelites are located in the sky, wich will help get a quicker gps fix.

Its possible to get a gps fix without internet, but it might take longer, and things like weather and buildings and such might have a big impact on how fast you get a fix.
The word you are looking for is "Satellite Cache" which will be downloaded (or better just recieved) from satellites at view.
This may take up to 12 minutes and at least 120 seconds.
The antennas power is pretty good as I get a fix in some buildings from reflection and/or direct signal. In case of A-GPS the onboard system downloads the cache from a server which has information from a nearby stationary GPS system. How does it know where you are? It knows the celltower-IDs around you.

Originally Posted by TiagoTiago View Post
Why is it so hard to calculate where the satellites are with reasonable accuracy? If you know their position in a point in time it's just a mater of doing some math to get their position at any moment in the future
Easy! No you can't! Why? If that would be possible you would get a fix in the second you get the ID of 3 sats.
The US military updates satellite's positions, some go offline for maintenance and come back up at another spot as one died and so on. Normaly you get a fix if you had one in the last 24h at the spot where you turned your gps off but not for sure. They are drifting and correction of positions are calculated constantly.

Please at least try to read on some information before you ask general questions on hardware and technical functions of things like "how does gps work?" Most of the hardware specs are at wiki.maemo.org... (just read the 100s+ thread asking about the IR device)
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