Vessel direction issue in OpenCPN

[Sea-and-Sea]

Boat is tied up but the direction/heading in OpenCPN keep changing, from any direction to any  It seems random, but i cant figure out why.  I see i have some duplicated items in the Data Browser and wonder if this could be part of the problem?  

I'm attaching my Data Browser data here in the hope that someone can spot my error please.




Any ideas please?
Colin

[PaddyB]

Boat is tied up but the direction/heading in OpenCPN keep changing, from any direction to any  It seems random, but i cant figure out why.  I see i have some duplicated items in the Data Browser and wonder if this could be part of the problem?  

I'm attaching my Data Browser data here in the hope that someone can spot my error please.




Any ideas please?
Colin

course over ground could be because the GPS is not moving, sometimes I´ll get a COG when stationary, though usually it´s Null. 
Were does  .Heading come from?  Looks like your AIS, does it have a compass?

[Boatingbaileys]

I also get this and have blamed my seatalk network for some time, however if I enable nmea as a plug-in and change the OpenCPN to use nmea rather thank SignalK it improves a lot.

[Techstyle]

It looks like you are only getting a heading or course over ground from the AIS source, and not the OP source 9 at least at the minute.  Either way GPS units often calculate heading either by:

• integrating the GPS signal (using consecutive signals and then calculating the direction based on the way that GPS position changes)
  
• using differential GPS which is basically 2 receivers.
  

both of which are troublesome when you are "stationary", first - are you truly stationary when tied up?  No; and secondly - is the repeatability that good that the position error would not invert consecutive positions or two receivers that are close together? no again.


if you don't want to just ignore it, then you could fit a compass/magnetometer, <$10 and can be fitted via I2C to the Pi or ESP32, or you could filter it out in software.

I would definitely set one of those GPS sources as priority though (if you haven't already)

[Sea-and-Sea]

ok - so i need to get my Moitessier HAT sorted to work with OP3. That will give me the compass data

This probably explains why i wasn't seeing this earlier with OP2.