[gpsd-users] Anomalous course / heading info from gpsdecode

[Roy Barkas]

I've noticed that on my system course data returned from gpsdecode is way out of whack with reported heading.

I understand that AIS units should source heading a mag compass and course from gps COG but they should more or less be close to each other.

I also understand that not all AIS transponders (and particularly class B units) will send course data.

When I get any course info at all (other than 0) from gpsdecode it's quite a bit different than the reported heading.

Examples from my log:

Msg type   3   Heading   80    Course 280

Msg type   3   Heading  207    Course 312

Msg type   3   Heading  220    Course   1

Msg type   3   Heading  306    Course 270

Msg type   3   Heading  231    Course   1

Msg type   1   Heading   16    Course 150

Msg type   1   Heading  321    Course 257

In the latest sample of 150 or so messages, almost all type 1's received have heading data but course is reported as 0.

In  type 3 messages, heading is always present but course is either mysteriously different or (mostly) 0.

I've checked my code - in all cases I'm taking the values returned as ['heading'] or ['course'] and just passing it through to the database without any manipulation.

Have I missed some important transform that I am supposed to be doing to either heading or course?

I'm still using the version of gpsd that is available from the Ubuntu repository (2.something I think).

Haven't yet met the challenge of building gpsd from source.

Cheers;

Roy