Tracking Hands

Currently, the Wii MotionPlus (WiiMot+) is capable of tracking its own movement in 3D space one-to-one. However, by conventional means it can only track this movement relative to the location it was at when the WiiMot+ was powered on. That is, if you held the WiiMot+ three feet above the ground, turned it on, made a motion, turned it off, turned it on again a foot higher and made the same motion, the WiiMot+ would not be able to tell the difference.

With 6DOF head tracking though, it is possible to tell the WiiMot+ exactly where it is located in 3D space regardless of when and where you turn the device on.


As you're aware from my previous posts, a 3IRLED 6DOF head tracker is capable of determining the exact position and orientation of the player's head in 3D space. Since the system knows the location of your head relative to the head tracker, it's possible to tell the WiiMot+ in-hand where its position in 3D space is by virtue of the fact that the in-hand Wii remote's IR camera has the same capabilities as the head tracker.

It's all a matter of relative perspective. As we know, the reason IR head tracking works at all is because conventionally the Wii remote detects the stationary sensor bar's IRLEDs as "moving" according to its own perspective and discerns where it's pointing from that.

The above image shows a stationary head tracking Wii remote and an in-hand Wii remote equipped with the WiiMot+. Both are pointing at a 3IRLED hat. The two boxes shown below the Wii remotes represent the approximate positions of the hat's three IRLEDs from the perspective of the corresponding camera. Because the system knows where your head is in 3D space courtesy of the head tracking Wii remote, any in-hand Wii remote can see the three IRLEDs on your hat and make the same calculations as the stationary head tracker to determine the location of your head in 3D space relative to that in-hand Wii remote. Since that in-hand Wii remote now knows your head's location relative to itself, it can determine it's own location relative to your head.

NOTE: The in-hand Wii remote only needs to be pointed at the IR hat during calibration.

Presto! The in-hand MotionPlus-equipped Wii remote now knows an initial position to start measuring one-to-one motion from. Naturally, this method can also be applied to "twomote".