It seems that the headtracking code already simulates a z coordinate by allowing you to get closer to the screen and the image gets bigger. That's done by calculating how far apart the two dots are from eachother.

If you're talking about a bit more virtual reality, then this video here would be pretty helpful.


He builds his own sensor bar with four dots in a 3D geometric setup. Depending on where the dots are, based on their perspective, it calculates a full 3D location.

Does that answer your question?

Well what he does in the video above (I'm no programmer, only a theorizer) is he has the left, top, and right dots on the same plane (the XY axis), and then he places the fourth dot further forward (on the Z axis). When the camera is looking at the sensor bar from the front, you get a diamond looking shape. When the camera is looking at the sensor bar from the side, then the Z axis dot (front middle) will move to the left and right quicker than the ones behind it. Make sense? Watch the video above at around 4:00. This is when he's just seeing the four dots on a black screen.

As for using intensity to calculate the Z axis, I think it would be possible (as can be seen if you play around with the sensitivity screen on the wii console) but it would be very very inaccurate. Blob detection (like used in the wiimote) will automatically adjust its contrast to make the brightest dots visible. You can see this in Johnny's finger tracking video HERE. When he reflects light off of his fingers without any reflective tape, the tracking picks up all the dots of light reflected and it's not accurate. When he puts the tape on the tip of his fingers though, the same amount of light is reflecting off of his hands, but the reflective tape is so much brighter than his skin that it only tracks the reflective tape. So therefore, the wiimote will automatically track the brightest object. Make sense?

Also, if you were to use only intensity to track the Z axis, then the LED lights would have to be exactly the same brightness every time. Since there are a number of different LEDS that people use, it just doesn't seem plausible.
Good idea though.

Another idea is to triangulate the location of a dot by using two wiimotes to watch the same dots from two different angles. This concept can be seen here in this video.

By the way, I have another question in this respect; it seems that John Lee's IR tracking system works pretty fine with 2 LEDs (rather than 4) and he is also using the perspective transmformation method. Given the fact, I am wondering if it's not easier (when it comes to mathmatical calculation) to do that with less noumber of LEDs ? how do you compare his method with the one in the video clip you just sent !

Thanks again!

Hi Wiweeyum!
I have seen the webpage and more detailed info is foud there, not yet so complete! I will contact him and try to get more precise information about the mathematics! Thanks for the tips!

I had really know idea about the flaw in John Lees project and I didn't know that it's not possible to look at an object via rotaing. Well, maybe it's beacuse that is not demonstared clearly in the video clip ! So basically what are you saying is that it works fine for Scrolling Left/Right and moving Far/Closed but NOT for Tilting, right!?

Wiweeyum, in John Lees C# code there are some variables related to IR-Data structure namely Size 1,Size 2,Size 3, Size 4. Could it be semehow related to IR-Size tracking that we discussed before?

Best,
       Yashar

 Hi!
I think I am now clear about the Geometrical mathematics that John uses to get the depth information. Infact, I think he is taking benefit of the knowledge that camera's Fie d of view if 45 dergrees or (pi/4): Given the fact, one can assume camera's field of view FOV=(pi/4) rad/pixel; And therefore for each dot postion, the corrsponding angle to the camera is easily found and having the angle and dot postion the z position is correspondingly derived! It's a very simple concept ; some useful information is given here :
http://blogs.bl0rg.net/netzstaub/2008/08/24/wiimote-headtracking-in-processing/

But I am not still sure about the other method that the guy in your video clip talks about. His method seems to be more complex with alot of nonlinear equations to be solved, but how the two methods differ is an interesting question for me and I would appreciate anyone with knowledge in this area to share it with us!

Finally regarding the code, I am trying to see how the Size variables are used ! The link I sent you says that the intensities are checked before the calcualtions are started which seems logical! But so far not so much similar is found tracks in the code !

What do you think!?