GPS Status vs Number of Satellites

redddevil · Occasional Visitor Joined: Jun 13, 2005 Posts: 28

Hi, having trouble reconciling the TomTom GPS status screen (which shows good connection to 7 satellites) with the 'bar indicator' which appears after a route calculation which shows 2 or 3.
Which is correct?
TFYH

julianbarker · Lifetime Member Joined: Apr 12, 2005 Posts: 431

IIRC the bars only start counting once you have a fix which happens at four sats. So a basic fix with four sats gives one bar, data from a fifth sat gives two bars, etc.

redddevil · Occasional Visitor Joined: Jun 13, 2005 Posts: 28

Thanks for the reply. I understand the correlation between bars and satellites but nevertheless the number of satellites indicated by the bars (post fix) both actually and by 'bar count' is always less than that shown by the GPS status page.

Synth · Posted: Thu Jul 06, 2006 10:18 pm Post subject:

Some satellites will be rejected for the calculation because they are too close to the horizon where errors will be greater.

redddevil · Occasional Visitor Joined: Jun 13, 2005 Posts: 28

That makes a lot of sense. Will the number near the horizon be random or fairly steady? I guess I'm asking what the satellite spread is like - I don't suppose they traverse the sky according to a fixed grid Question

lbendlin · Posted: Fri Jul 07, 2006 12:01 am Post subject:

the sats circle the earth every 12 hours. The constellation is very dynamic. Use a program like VisualGPS and let it run for a day - it will show you the trajectories.
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