APB Heading vs Bearing

[Onno]

I noticed that in the APB sentence we are using field number 13: Heading to steer to destination waypoint.
Should it not be more logic to use field number 11 Bearing, present position to destination because we are in GPS mode?

[seandepagnier]

Field 13 is where the autopilot needs to steer. I am not sure why you think this is more logical?

[Onno]

Wel first a Raymarine plotter does not send the heading to waypoint if no electronic compass is connected. so the only course we would be able to use would be the "Bearing"
Second when using a waypoint it make sens you are steering on COG in GPS mode I would cal that Bearing in this correlation vs Heading.

[ironman]

I would reconstruct the APB handling as follows: if Bearing Origin To Destination (8, 9) is provided in the APB sentence plus an XTE (3, 4, 5), the autopilot applies a correction for the XTE, like pypilot does with apb.xte.gain. If you provide Heading To Steer (13, 14), like OpenCPN and the autopilot_route plugin does, the autopilot disregards the other fields but steers this heading-to-steer instead. This way, you can cater for the raymarine consumers who want to try to use the dumb xte based steering, but also the enlightened opencpn users and even more enlightened autopilot_route plugin users. EDIT: This reconstruction is my interpretation of the superfluous fields present in the APB sentence, and my suggestion for how pypilot should handle this superfluousness.