I'm working with an MPU 9150 device mounted inside a Myo armband. The device provides IMU measurements comprising linear acceleration, angular velocity and quaternion orientation. The quaternion expresses an orientation of the moving frame attached to the device (we can call it 'myo_frame') with respect to a fixed Earth's frame. The acceleration is expressed wrt its own moving frame, that is an ENU frame (x-East, y-North, z-Up). I need to express the same acceleration wrt the myo_frame. Does anyone know which is the rotation required to achieve that? I know from the datasheet of the MPU 9150 that the internal magnetometer uses a NED frame (x-North, y-East, z-Down), so I thought that the rotation from NED to ENU was the one required. But apparently it doesn't look like so.