How many satellites are actually used to get position?

Question

NMEA 0183 Version 4.10 defines that there cannot be more than 12 satellites in GGA message:

Number of satellites used (range: 0-12)

But there can be more active satellites defined in GSA:

satellites used for navigation, and DOP values

So how many satellites are actually used to calculate position?
See example:

$GNGGA,155000,4700,N,03201.46451,E,1,12,0.78,9.5,M,27.7,M,,*4E 
$GNGSA,A,3,21,18,20,16,10,15,27,08,32,,,,1.27,0.78,1.01*11
$GNGSA,A,3, 68,83,76,69,85,,,,,,,,1.27,0.78,1.01*11

12 satellites in GGA
14 (9+5) satellites in GSA

max5555 max5555 · Answer

I have found the answer:

When the NMEA standard was created many years ago no one was expecting
  anyone could use more than 12 satellites for resolving location
  because the number of satellites visible at once was less than that,
  thus the GAA message was limited to 12 SVs. Now with our fancy
  multi-constellation receivers it’s very common to have a lot more than
  12 SVs but those receivers have to be backwards compatible with older
  NMEA versions (currently 4.11) thus they limit the GAA SVs field to 12
  but in the newer GNS field it can go up to 99.

https://github.com/mikalhart/TinyGPSPlus/issues/52

How many satellites are actually used to get position?

One Answer

Add your own answers!

Ask a Question