How do I access the GPS Expansion data?



  • It seems like common Linux packages like gpsd are not available through opkg yet, nor is there a tutorial in the wiki how to get the actual position with the GPS Expansion.

    Did anyone achieve it to get the GPS Expansion running with the Onion Omega?

    I can confirm that the GPS Expansion is working correctly since I was able to test it on my Windows PC.



  • I didnt even know that the GPS Expansion was already shipped? Still waiting...
    Also interested how to read the coordinates!



  • @Peter-Harrald I found this post which describes how to access the gps data via serial interface: https://community.onion.io/topic/515/gps-expansion



  • @Benjamin-Rau Thank you very much for showing me this thread.
    I can confirm that there is some data accessible via cat /dev/ttyACM0
    Unfortunately the data seems not to be formatted as described in the NMEA standard (see the stackoverflow link referred to in the post).
    Even if the receiver finds five and more satellites (according to the five $GPGSV lines in the result), the $GPGLL remains almost empty. Additionally even the example in the post you mentioned seems not to fit to the standard. According to this site, $GPGLL should contain Geographic Position, Latitude / Longitude and time. Instead in the example it contains just one number and a V (whatever this means)

    Does anyone have an idea who to get an actual position out of the data?

    Example Data:
    $GPRMC,,V,,,,,,,,,,N*53
    $GPVTG,,,,,,,,,N*30
    $GPGGA,,,,,,0,00,99.99,,,,,,*48
    $GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30
    $GPGSV,6,1,21,01,,,24,02,,,23,05,,,23,06,,,25*7C
    $GPGSV,6,2,21,07,,,22,08,,,24,09,,,23,10,,,25*79
    $GPGSV,6,3,21,11,,,23,13,,,23,14,,,22,15,,,25*7B
    $GPGSV,6,4,21,16,,,23,20,,,26,22,,,23,23,,,28*72
    $GPGSV,6,5,21,24,,,29,25,,,24,26,,,24,27,,,25*75
    $GPGSV,6,6,21,28,,,24*76
    $GPGLL,,,,,,V,N*64



  • Unfortunately i feel more like an integrator rather than a developer ;)

    But when interpreting:
    $GPGGA,,,,,,0,00,99.99,,,,,,*48

    I think your gps doesnt have a fix yet, and without gps it wont send data.
    The fix has to be 1 (one), instead it is 0 in your example.

    Mine (not the one from Onion team) took quite long the first time to get a fix.
    I can compare the raw output of mine this night. In the meantime you could try to get a fix ;)

    Right now i think the output follows the standards.

    Cheers Ben



  • I believe Benjamin is correct. Those sentences are in fact NMEA compliant and indicate no fix yet. Received my receiver from onion.io last week and it took about 20 minutes outside for TTFF and went full 3D. After than cold restarts using u-center it only took seconds to hit 2D fix.

    You may be able to speed it up by using u-center's AssistNow and push the almanac manually.



  • @Peter-Harrald Btw https://github.com/jamesp/node-nmea is a pretty nice library for parsing nmea data.

    https://github.com/omcaree/node-serialgps would be even better, if you dont want to read the data from the serial yourself. Unfortunately the dependency "serialport" needs compilation, which is not possible without npm.

    And here how i read gps data (because "cat" is not working for me):
    https://gist.github.com/benjaminrau/a0ea133786e950deb7ee


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