The UNC Tracker Project

6D Pose Estimation for Humans and Devices

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Head-mounted displays (HMDs) and head-tracked stereoscopic displays provide the user with the impression of being immersed in a simulated three-dimensional environment. To achieve this effect, the computer must constantly receive precise six-dimensional (6D) information about the position and orientation or pose of the user's head, and must rapidly adjust the displayed image(s) to reflect the changing head locations. This pose information comes from a tracking system. We are working on wide-area systems for the 6D tracking of heads, limbs, and hand-held devices.

In April, 1997 the UNC Tracker Research Group brought its latest wide-area ceiling tracker online, the HiBall Tracking System. The system (shown in images above) uses relatively inexpensive ceiling panels housing LEDs, a miniature camera cluster called a HiBall, and the single-constraint-at-a-time (SCAAT) algorithm which converts individual LED sightings into position and orientation data.

The HiBall Tracker provides sub-millimeter position accuracy and resolution, and better than 2/100 of a degree of orientation accuracy and resolution, over a 500 square foot area. This is the largest tracking system of comparable accuracy. The HiBall Tracking System is being sold commercially at this time.

Here is a HiBall slide presentation from ACM VRST 99.

Motivation for Wide-Area Tracking

Certain virtual-environment applications can benefit from long-range trackers. We believe that exploring an architectural model by walking is more natural and less confusing than exploration by flying or steering treadmills. For example, using the UNC wide-area optical tracking system, one can walk inside a model of Professor Fred Brooks's kitchen, where the scale of the virtual model is 1:1 with reality. We believe this method of exploration provides a better understanding of the model than unconstrained flying, which distorts the user's sense of scale and space.

Another important reason for long-range tracking is that augmented reality demands this capability. Most HMDs are closed-view, preventing the user from seeing the real world outside. In contrast, augmented reality uses see-through HMDs that let the user see the real world while simultaneously superimposing on or compositing 3D virtual objects with the real environment. Ideally, it would appear to the user that the real and virtual worlds coexist. Augmented-reality applications use the virtual objects to convey information that the user cannot detect with his or her own senses. Potential applications include giving doctors "X-ray vision" into their patients (by superimposing 3D MRI or ultrasound data onto the patient's anatomy) and aiding assembly and repair of complex 3D equipment with schematic overlays. Augmented reality, however, imposes much stricter requirements on the tracking system than virtual-environment applications do. Augmented reality requires highly accurate trackers because even tiny tracker errors cause noticeable misregistrations between real and virtual objects. Also, augmented reality demands long-range trackers because "flying" is meaningless. In a closed-view HMD, we can create the illusion of flight by translating all the virtual objects. In augmented reality, however, if a user wants to see the other side of a real patient, he must physically move himself and the HMD he wears, and this requires long-range trackers. Much more work needs to be done to improve tracking systems before augmented reality becomes a practical technology.


The HiBall Tracking System is being marketed in a joint venture between UNC Chapel Hill and a local company, 3rdTech. For more information, see the 3rdTech HiBall web page.


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Last content review: July 10, 2000
Last update: Wed, Aug 27, 2008