Just an idea...
As we have telemetry running via frsky and some other systems, is it possible to use the position data, if available, for forwarding them to a dedicated Arduino our whatsoever via trainer port and use them to calculate the pan and tilt angle for the tracking system? I could imagine that the initial heading and position of the pan axis has to be the same as (or pretty close) of the copter...from this point on they're synched and the copter can be moved. By that way you don't need additional hardware on the ground such as magnetometer or gps.
I guess it's related to the tx you use but as I'm not the only one using frsky or the hacked th9x (currently with open9x) with frsky there's got to be some interest...no?
Please correct me if I'm wrong or if this nothing new to you and I must have missed it somewhere
Thanks in advance