I have been setting up my new SimpleBGC 32-bit gimbal and have been learning about how the hardware and software works.
It is my first gimbal that that has a slip ring so it can do unlimited yaw rotations.

I see that the controller does not have an encoder or any method to determine 0 deg yaw relative to the UAV. I have tried the yaw follow method but unless the gimbal is aligned on start-up it is not the most reliable.

When the Pixhawk - MAVlink interface is supported by the Basecam code ( which I believe is soon) , I can see a simple solution to keeping reference between the gimbal yaw and the UAV.
1) Plug in a I2C Based compass to the gimbal controller and attch it to the gimbal.
2) Include a compass calibration routine in the firmware.
3) The gimbal controller obtains UAV magnetic heading by reading the MAVlink messages
4) The gimbal controller works out its heading and the difference between the UAV and gimbal.
5) If in follow mode, the controller adjusts its heading to match the UAV.

We would now have the ability to tell the gimbal via the serial interface hold a particular heading, pitch and roll no matter what the heading is on the UAV