The AR Roadmap spin-off prototype we built for BMW Research in 2004, relied on tracking a large number of items equipped with (passive) infrared reflective markers. We used high-end tracking cameras built by advance realtime tracking GmbH, capable of tracking a high number of markers with good resolution/precision.
If you would like to play around or even build your own homegrown AR system, Johnny Chung Lee from CMU's Human-Computer Interaction Institute, shows how to use components of Nintendo's Wii game console for active marker-based tracking. The WiiMote is used as tracking device, transmitting location data of active LED markers, as for instance the Wii sensor bar, to a PC via Bluetooth. His C# SDK and more info on his approach are availabe via his project website.
The results are impressive, well unless you need surgical precision, but then again that can easily cost you 10K+ USD/EUR.
Enjoy Johnny's video on the head tracking system built by utilizing the WiiMote.
