See "Pure IMU-based Positional Tracking is a No-go"[1], a position from an IMU starts to drift in a fraction of a second and than shoots off into infinity. With

See "Pure IMU-based Positional Tracking is a No-go"[1], a position from an IMU starts to drift in a fraction of a second and than shoots off into infinity. Without an absolute reference there is nothing you can do to stop it and the errors will accumulate. It's not just a little bad, it's completely unusable. A further complication is that the IMUs you find in phones, especially back when all this was new, weren't very good. So even a plain 3DoF experience would suffer from slow response and yaw-drift from lack of magnetometer, which is why GearVR had an extra IMU in the headset and why Daydream required new certified phones with better IMUs. 3DoF can still be good enough for VR180/360 movies, which don't allow movement to begin with. But as far as gaming is concerned, you really do need 6DoF, as even a bit of leaning forward in a chair will make it instantly obvious that the headset motion and the headset visuals are out of sync. [1] https://www.youtube.com/watch?v=_q_8d0E3tDk https://www.youtube.com/watch?v=_q_8d0E3tDk