good point, I'll be waiting for Devedander's inevitable response
Here it is.
I have a feeling that it's not quite what most here are thinking and isn't like the rfactor tracking. Most games, although drawn in 3D are on a flat screen and the image of a scene remains the same on the screen no matter what angle the screen is viewed from. headtracking allows you to look at the screen as if it's a window, if you stand up/raise you head you can look down through the window and see more of the ground or floor in front of you or if you move closer to it you can see a wider field of view. I suspect if it is used that it'll be a lot more subtle than trackIR and will be more a visual cue for the brain to interpret the image as a more convincing 3d world rather than for looking around the cockpit.
I actually already covered this response earlier but in short:
This seems like it wouldn't be very useful in a driving game because... well imagine it in action. How would you use it?
The looking through a window method means that as you move your head to the left, you see more out the right side of the window. What's more, in order for the illusion to work, the movement will have to be 1:1 vs the movement of what you see on screen. Whats more this is not a head rotation tracking method (although it could be but you then run right back into the issue of TRACKIR dissorientation) so it's a lot like the left analog stick on an FPS game in terms of how it changes your view point. In an FPS you actually move using the left stick so it's not really the same, but if you are looking across any significant distance, the effect is very similar. Take COD4 for example, look across a large open area of the map. Move the left stick to the left. See how your view changes? That's similar to the looking through the window method of head tracking.
So try this:
Sit in your car and make a little box out of your hands (movie director style how they frame stuff). Hold it a few inches in front of your face so it replicates about your field of view in a racing game. In order to simulate the view change of your tv in "window" mode of head tracking, you must keep your face looking forward. Yes in real life you would turn your head down and right and look out the bottom right of your "window" but you can't do that on your TV... below and to the right of your TV is... no TV so there is no picture to see.
Now move your head so that you can see your stick shift.
Remember to keep your hands stationary while they form the "window". This is because unless your TV can move down off the wall to where you are looking, that is what you will be dealing with while using head tracking. Also remember keep your head facing forward because we aren't dealing with tracking you turning your head (this is again the TRACKIR method, introduces problems and isn't accurately represented by using a frame in front of your face because what's behind the frame here is actually 3d, on your TV it isn't).
How did you have to move your head? To lood down and right, you have to move your head way up and left.
Want to see your left rear view? You must move your head way over to the right.
This is how wii head tracking works and is the non TRACKIR method.
You game "window" always looks forward, you just change the angle at which you look through it.
Now you could try to mesh this with some kind of head tracking of how you turn your head also, but that brings you right back to the problems of the TRACKIR method.
I know you guys all thing I am being a wet towel here and trying to rain on your parades, but it's truly just how it is. Like I said I have tried head tracking a log over the years, and so far the problem with head tracking is that the display stays put. This makes turning your head style head tracking dissorienting especially in fast paced environments like racing. I thought initially just like you all probably do that this would be awesome and be just like VR and totally be a natural extenstion to looking at games. Well in some ways it does work out that way, but in many circumstances it just doesn't.
The wii head tracking style where your TV becomes more of a window is a lot less dissorienting, but you will find that at any decent distance from a display which is of any decent size, you have to make very large movements to significantly change your angle of view in the game.
http://www.youtube.com/watch?v=Jd3-eiid-Uw
There is the original wii head tracking video. Around 3:35 he starts showing the window method of head tracking. Imagine that instead of looking at a football stadium, he is looking at the cockpit view from a car. Now where would the stickshift be? Down to the the right somewhere... watch as he moves around and figure out what he would have to do to see down and to the right. He already moves quite far with his "head" in the video and if that was a car view, it woudln't be nearly enough to see the stick shift or a rear view mirror or anything.
Here is the wii style head tracking in use. This is actually more full body tracking, but where your head goes yoru body follows so the result is very similar to head tracking. This is an old arcade game called Police 911.
Starting about 3 minutes into it you can see what I am saying about having to move your head to significantly change your view, and you will see that as the view point changes, you don't get to see stuff immediately around you so much, you see stuff that was off to the sides in the distance.
http://www.youtube.com/watch?v=PcfUE4ZcqRI
So yes, if it's used, it would be more subtle and natural to help you feel the 3d of the game, but it would not allow you to see things outside your normal field of view with much ease.
