Working through configuration of an Alexmos gimbal, it appears that for ArduPilot to command the gimbal to “point camera here” (ROI) that the gimbal needs to have a magnetometer installed on the camera bracket.
Without it, I’ve found that the only way “point camera here” works with Alexmos is if the copter and gimbal are initialized facing “north.” And then I suspect there would be significant drift.
I don’t recall seeing this requirement when testing a Storm32 gimbal controller - I’m going to have to go back and check.
I had assumed that the ArduPilot simply used the gimbal’s home position and commanded appropriate gimbal pan/yaw offset to aim at the ROI. It sure would be nice to see some sort of tech article about this topic.
For a copter that can yaw independent of flight path, it might be easiest to configure a gimbal as a two-axis device only - and use copter yaw to point the camera - and command the gimbal to tilt to aim at the target altitude. No help for other vehicle types.
Actually - since few gimbals are setup to allow full 360 degree yaw - using copter yaw is the only guarantee a camera could be aimed in an automated mission.
As I recall in past tests of copters without a gimbal on missions using ROI and WP_YAW_BEHAVIOR that the ROI superseded WP_YAW_BEHAVIOR. Since the yaw limits of the gimbal are entered as parameters, it would be nice, but perhaps overly complicated, to have these two functions work together. That is, use the gimbal as far as it can - and then yaw the aircraft the rest of the way if necessary point the camera at the target.
I don’t see much written or asked about gimbal usage these days - I’m guessing it’s become tribal knowledge for the old-timers who worked through it, and new guys just fly DJI and don’t bother.
If someone can help me get a better understanding of these facets, I’d be happy to write up something to add to a wiki or doc.