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-   -   Why does my N900 look for internet connection to use GPS? (https://talk.maemo.org/showthread.php?t=61421)

srydy 2010-08-30 19:01

Why does my N900 look for internet connection to use GPS?
 
I called Nokia support and was told that N900 is not a real GPS device hence it requires an internet connection.

NokiaRocks 2010-08-30 19:04

Re: Why does my N900 look for internet connection to use GPS?
 
That's not true for sure. It just takes ages to get an sat-fix w/o a-GPS.

festivalnut 2010-08-30 19:06

Re: Why does my N900 look for internet connection to use GPS?
 
i think we have assisted gps, it uses the internet to get a rough location, cutting down the time it takes to get a satellite connection since it knows where to look (i generally think 'up' is the correct direction to look for sattelites, but what do i know.)

mthmob 2010-08-30 19:08

Re: Why does my N900 look for internet connection to use GPS?
 
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.

tirtawn 2010-08-30 21:51

Re: Why does my N900 look for internet connection to use GPS?
 
Quote:

Originally Posted by mthmob (Post 802537)
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.


This is the key. If you use the assisted gps using internet, it will help to get the current position within seconds rather than "minutes".

TiagoTiago 2010-08-30 22:53

Re: Why does my N900 look for internet connection to use GPS?
 
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 (the far the two moments are the worse the accuracy is, but i wouldn't expect it to get too bad in just a couple of days, and whenever there is a connection to the internet it can re-zero the positions to a more accurate measurement.

Joorin 2010-08-30 23:18

Re: Why does my N900 look for internet connection to use GPS?
 
Quote:

Originally Posted by TiagoTiago (Post 802733)
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 (the far the two moments are the worse the accuracy is, but i wouldn't expect it to get too bad in just a couple of days, and whenever there is a connection to the internet it can re-zero the positions to a more accurate measurement.

Are the satellites geostationary? If that's the case, you can't do any math to find them. Then you need to get some other fix, like using 2G/3G antennas.

TiagoTiago 2010-08-30 23:22

Re: Why does my N900 look for internet connection to use GPS?
 
No, they spin around the earth in a spherical constellation all at pretty mucht he same altitude; it's fun to watch speed up animations of them going around trying to figure out the path of a single one, it's kinda an optical illusion, kinda looks like they will collide or make an extreme turn when reaching the poles.

gunni 2010-08-30 23:27

Re: Why does my N900 look for internet connection to use GPS?
 
Quote:

Originally Posted by TiagoTiago (Post 802733)
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 (the far the two moments are the worse the accuracy is, but i wouldn't expect it to get too bad in just a couple of days, and whenever there is a connection to the internet it can re-zero the positions to a more accurate measurement.

I think the problem with this calculation is that the clock of the N900 would not be accurate enough. You can calculate the position of the sattelite, but you never know if your "now" is exactly the same as the sattelites "now".

TiagoTiago 2010-08-30 23:37

Re: Why does my N900 look for internet connection to use GPS?
 
I wouldn't expect the error in the position would be big enough to make the result of the calculation useless.

btw, here is an animation of the satelites orbiting:

http://upload.wikimedia.org/wikipedi...llationGPS.gif
(in this one the effect i mentioned in my previous post isn't noticeable_

according to the source it says time is sped up 2880 times making one day go by in 30 seconds, and the time of a single orbit of a single satelite is 12 hours, i think those numbers would probably be enough to calculate how many degrees per minute the satellites move in the sky.


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