General GPS Question

Abdelrazak Younes younes at
Fri Oct 31 07:57:22 CET 2008

On 30/10/2008 19:44, Matthias Camenzind wrote:
> I thought right now near same like you. I thought about the speed of satellites,
> But also right now i had another idea. With the signal form two satellites, and a
> known high over sea it should be possible to locate you on north or south of
> earth (only two possibilities).
> This would be nice if you go on a mountain and you are standing in front of a
> "signpost" (google translated) with meters over Sea value to get faster your first fix.

You won't get a faster first fix because you concentrate on two 
satellites. The ublox receiver is able to track up to (AFAIR) 16 
satellites at the same time. The *main* way to speedup the TTFF is to 
have almanac and optionally ephemeris available on the FR. Almanacs are 
valid for one week so it's easy to make sure you have up to date almanac 
before you go on a mountain :-)

> A simple
> question "Are you in the North of earth?" would be enough to get only one possibility.

Unless you did a long plane travel before switching on your FR, the last 
known position would be enough. Many satellites will be visible in 
Madrid and in Paris at the same time for example.


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