nzvideoguys said:
This declination shouldn't come as a surprise to DJI, we all went thru it with the combo mag/compass thingy, rotate puck according to your magnetic declination, Done!
Exactly! The solution coming from DJI back then was to rotate the compass. Sadly, very few of the beta testers here seem to be aware of this as they've probably never flown anything but a Phantom, (I could be wrong). I also bought up the point about dialling in the X Y and Z distances, as these values are defaulted at "0" on the Phantom software, which, when accurately measured, is not their true position. The GPS on the Phantom is located in the centre, under the plastic body shell, and the compass is way down on the right rear leg. If we had a version of the software where the XYZ values could be changed to reflect their actual position, we may be a step closer to solving this complicated riddle.
Most of us are aware that other Naza platforms rotate the compass. DJI advises not to rotate the compass on the P2. Rotating any compass to an off axis position, P2 or not, is generally a bad idea unless the software compensates for it. When you rotate the compass off axis, you have at least two axes that no longer have the correct sensitivity because they aren't aligned with the orientation of the vehicle. As result, you wind up with inaccuracies. When you apply a tilt compensation algorithm to the compass heading it gets worse as the compass is not moving through the same axes as the vehicle. I would suspect a number of very expensive fly aways on DJI's higher end platforms may have been caused by this.
The right way to correct for declination is painfully simple: You have a lookup table of declination data which is roughly 3Kb to 4Kb in size and based on GPS lat/lon. Once the GPS position of the vehicle is known, the corresponding declination is pulled from the lookup table and applied to the magnetic heading. It's about 3 lines of code and a 2 axis table. Pretty simple. My suspicion is that the P2 Naza is actually doing this but it is applying it backwards (i.e. subtracting as opposed to adding) which is why many have to rotate their compass by roughly twice their declination.
Anyway, rotating the compass is not very smart on any platform. At best, it's a work around to a problem that shouldn't exist.