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GPS data not interpreted

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  • GPS data not interpreted


    I have all the required components for Designator and Map Monkey however my GPS data, which I am simulating, fails to register anything in the program. If I use the advanced GPS settings the speed changes relative to the data however satellites in view shows 0 when it is actually 7 and the current position is not displayed.

    Can anyone point me in the correct direction to fix this problem?

    For those interested I am simulating the NMEA data from a file that I created from using a Trimble GPS module I obtained for a university project a few years ago. I am sending the $GPGGA and $GPVTG lines every second to the computer running Map Monkey via a serial cable (null modem). I know the data is being received properly at the serial port as I have checked it in hyper terminal.

    I have tried using the following bit rates
    4800 8N1
    and 9600 8N1

    Any help appreciated.
    Thanks in Advance

  • #2
    I dont think your sending the right lines.. On freerive I use the $GPRMC for the Long / Lat / Speed and heading.. and the $GPGGA for the sats and altitude.. I am unsure what mapmonkey uses but I would of thought they will be the same as mine.

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    • #3
      The NMEA 0813 standard specifies the following sentences

      $GPGLL Geographical position, latitude and longitude
      $GPGSA GPS dilution of precision and active satellites
      $GPGSV GPS satellite in view
      $GPGGA GPS fixed data
      $GPRMC Recommended minimum specific GPS/TRANSIT data
      $GPVTG Track made good and ground speed
      $GPZDA Time and date

      In theory Map Monkey / Destinator 3 should be able to handle all of them to be compliant. Unfortunately I don’t have the module to try it with those sentences mentioned. However you mention that GPGGA is used to determine number sat's in view. I'm outputting this line and it is not shown correctly.

      The majority of GPS units I have experienced output the $GPGGA and $GPVTG by default as they give the information that is generally required. Surly map monkey supports these! Anyone shed some light here?


      • #4
        Mappoint support in RR only uses RMC and GGA like FreeDrive does. The GGA satelites has nothing to do with the sats in view, but it is the number of sats used in calculating the fix. Most GPS devices will send RMC, GGA and GSV .. the other ones vary in presence/frequency from what I've seen.
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        • #5

          Looks like that was the problem.
          I modified my file and made up some $GPRMC strings based on my data in the $GPGGA and the position moved to the correct point in Map Monkey. Not sure on what is needed for the satellite view to be correct but I guess I'll just have to worry about that one when I get it going in my car.

          A little disappointing as my data is useless for testing, but thanks for the help guys!