Valve style marker tracking
If anyone is interested, I made a system 2 years ago which basically does what Valve is doing using markers for the head tracking. It is open source and you can find it here:
http://forum.unity3d.com/threads/108256-Unified-Coordinate-System-for-String-and-QCAR
You will need the StudierStube tracker engine if you want to use it on Windows instead of using Vuforia on IOS or Android.
http://forum.unity3d.com/threads/108256-Unified-Coordinate-System-for-String-and-QCAR
You will need the StudierStube tracker engine if you want to use it on Windows instead of using Vuforia on IOS or Android.