Definition of terms requested.

[David Taylor]

Where can I find a definition of these terms as used in cgps?  Or what do the 
terms mean?

- number of satellites visible?
- number of satellites used?

I don't know whether these values are computed inside gpsd, or whether they are 
simply direct copies of the data sent from the GPS receiver itself.  The more I 
think of it perhaps the GPS receiver is responsible for the numbers...

Background:

I ask because I recently moved an antenna about one foot higher to a slightly 
less shielded location (both indoors), and noticed a decrease in the number of 
satellites used, but with an increase of the number of satellites visible, 
accompanied by an increase of the average SNR.

  There are graphs at the bottom of this page:
  https://www.satsignal.eu/mrtg/performance_raspi-13.php

I had (incorrectly) expected that the number "visible" would simply depend on 
the latitude and longitude of the observer, and should therefore be independent 
of antenna height or local obstructions.  So does "visible" include some SNR 
threshold somewhere?

Given that the location is a little better I expected an increase in SNR.

I don't understand the decrease in the number of satellites "used".

It's a MAX-M8Q-0-01.

Thanks,
David
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