Mechanic, the castAR can follow many tracking targets - this allows a builder to construct a dome or other enclosure that you can be guaranteed of never losing head tracking - the tracking camera on the castAR has a 110 degree FOV, so if you place tracking target (basically five IR LEDs) every 90-100 degrees along both axes, you're set. The goal for the integrated IMU was met so even if the tracking camera manages to lose all the tracking targets, the IMU can take over until such time as the camera can re-accquire a tracking target.
I did some digging and I really don't care for being compared to this Voss dude. I'm certain that every statement I've made here can be easily and independently verified by anyone here that cares to click the links I've provided. Or better yet, search YouTube and Google for "castAR" and see what you get.
g.