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Imu.compass vs GPS Compass
#1
When I look at my boat graphic in OpenCPN it is constantly spinning, When I look at the instruments in OpenCPN (GPS Compass) it is varying all over. Looking at Signal K, this could be navigation.courseOverGroundTrue - which varies all over the place in SignalK. The  Imu based IMU.compass (navigation.headingMagnetic?) seems to be stable to the second decimal place when I look in both Pypilot and SignalK. I am currently on land, will this correct itself once I get sailing or should I be looking at the IMU data In OpenCPN?
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#2
As I'm sure you know, your position and heading with GPS varies continuously when you are sitting still. I've been troubleshooting another GPS-related problem while sitting at home, and turned tracking on OpenCPN, the track is all over the place, within less than .01 Nm. It's just position drift from your GPS. GPS can't do course without movement - it uses the last two position reports to estimate course. Speed is estimated using either differential between position reports or Doppler shift. So yes, it will sort itself out when you get on the water.
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#3
It makes sense.  I did turn on some other sentences in SignalK to NMEA0183 plugin and then OpenCPN seemed to use this for the own vessel graphic and showed the extension to show direction (see pic).  this seems to be very stable


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