[RyanCahoon]

There have been teams that have done something related, in that when using an omnidirectional drive they had the strafing be independent of robot orientation (and then spin was controlled separately): pushing the joystick in a direction would always make the robot move that direction with respect to the driver station. This sounds like essentially the same task you're tackling.

The usual approach those teams used is to try to track the robot orientation using a gyro, but since you only get angular velocity from the gyro, you end up with accumulating error in your angular position measurement. Some people have tried using a digital compass, but the usual reported result is that there's enough ferrous material in the field and the robots (not to mention magnetic fields from the motors) that these don't work.

Something you might consider instead is having a set of buttons that would command the robot to turn predefined angles (90* 180* -90* etc) using the gyro, that way you wouldn't have the problem of long term gyro drift.

--Ryan