$GPGSA, $GNGSA, $QZGSA - GNSS Active Satellites and DOP

Prevents proprietary source code from being provided as customer documentation

This sentence provides details on the nature of the fix. It includes the numbers of the satellites being used in the current solution and the DOP. DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix. It is a unitless number where smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to be a perfect number. For over determined solutions it is possible to see numbers below 1.0. There are differences in the way the PRN's are presented which can effect the ability of some programs to display this data. For example, in the example shown below there are 5 satellites in the solution and the null fields are scattered indicating that the almanac would show satellites in the null positions that are not being used as part of this solution. Other receivers might output all of the satellites used at the beginning of the sentence with the null field all stacked up at the end. This difference accounts for some satellite display programs not always being able to display the satellites being tracked.

If multiple GPS, GLONASS, etc. satellites are used, separate GSA sentences with different talker IDs are sent.

  $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39<CR><LF>
   1     2 3 4                     5   6   7

Where:

  • 1 - Sentence identifier. Can be one of:
    • GPGSA - GPS
    • GNGSA - GLONASS and GPS
    • QZGSA - QZSS
    • IMGSA - IMES
    • BDGSA - BEIDOU
  • 2 - Selection of 2D or 3D fix:
    A = Auto selection
    M = manual
  • 3 - 3 = 3D fix - other values include:
    1 = no fix
    2 = 2D fix
  • 4 - PRNs of satellites used for fix (space for 12)
  • 5 - Position Dilution Of Precision (PDOP)
  • 6 - Horizontal Dilution Of Precision (HDOP)
  • 7 - Vertical Dilution Of Precision (VDOP)
  • CC - checksum
 All Classes Files Functions Variables Typedefs Enumerations Enumerator Defines