I’m going to have to dig a bit to find my references at the time, but I posted about this situation here:
Searching just now, the Alexmos documentation on the magnetometer doesn’t address this particular issue - so I’m not exactly sure where I got this idea. Alexmos magnetometer docs: https://www.basecamelectronics.com/files/v3/SBGC32_Magnetometer_eng.pdf
What I do remember is that on my workbench, Point-Camera-Here didn’t work with Alexmos with MavLink. The gimbal was directed to an incorrect azimuth. This is what led me to the learning a magnetometer was required.
Calibrating a magnetometer mounted under a camera is also problematic - so after installing a magnetometer, I don’t remember testing it in flight.
It was peculiar because ROI does work fine - but it’s not yawing the gimbal, it’s yawing the whole copter.
I tested it here with 5 different ROI’s on a flight: https://youtu.be/DqwfeYNyV4Y