Rotation and heading

[Oni]

Sorry if this was discussed, but even after search I can't find quick solution for this problem: when I try to get "global heading" of vehicle (0 to 359 degrees in relation to Z axis) with getVehicleRotation it gives me unexpected values in case if there is rotation along other axes. For example, if Hydra flies straight to the north, this function gives me "0" as I expect, but if I make half roll (continuing to fly in same direction), it inverts the result, giving me "180". Any way of calculating "global" heading via returned values? Or I just use wrong function? Of course there's a way of capturing two positions within small time interval and using arctan to get angle, but maybe native solution exists?