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48623magnetic declination

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  • dpa_io
    Aug 20, 2014
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      Cross-posted from the DPRG list:
      For those working on outdoor robots navigating to GPS coordinates using 
      a magnetic compass or IMU-based magnetometers, the difference between 
      magnetic north and true north needs to be incorporated into the heading 
      In the before-time, the local magnetic variation was included in the GPS 
      NMEA $GPRMC sentence in fields 10 and 11, but that no longer appears to 
      be the case.  My GPS currently returns zero for both of those fields, 
      and Steve Edwards confirmed this with his GPS at the last RBNO.
      I think the GPS satellite guys just got tired of having to upload new 
      magnetic maps all the time.  Too bad
      So it looks like for jBot the magnetic variation will need to be entered 
      by hand for any particular location.  That change has now been  made to 
      jBot's navigation code.
      There's probably an app for your GPS-equipped smartphone that can return 
      the local variation, but I haven't found a good one.  In the meantime, 
      the NOAA website at:
      provides a calculator that allows you to enter a lat/lon (and date!) and 
      returns the correct magnetic variation.  For the SMU campus in Dallas it 
      currently returns 3.58 degrees E (i.e., add 3.58 to your compass 
      heading) and says it changes by 7.5 minutes per year.
      Anybody got a slicker way of automating this process?

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