3.2 Tracking the Actors

 Setting up the tracking system required two cameras, two PC's (one for each

camera), colored paper or cloth for the straps, and sufficient USB or Firewire cable to

accommodate the setup. The tracking system worked under different lighting conditions

provided adequate training is performed on each camera. Training consisted of acquiring

many pictures of each strap and the background and determining the range of the colors

that belong to each strap. An application provided with the tracking system

accomplished most of this process.

 Two sets of straps were created for the system. The first set of straps consisted of

colored pieces of paper fastened with tape. These straps were used in the first study and

the participants suggested using a different material because the paper was

"uncomfortable and sometimes distracting." The second set was constructed with

colored pieces of felt to increase the comfort level of each participant. These straps were

fastened with small strips of Velcro. Figure 3-1 shows the second set of straps attached

to a participant.

 The tracking system on each PC then transmitted the two-dimensional coordinates

of each strap to a client computer. Tsai's camera calibration algorithm is used to

calibrate each camera and recover extrinsic and intrinsic camera parameters [24].

Calibration was achieved by explicitly mapping two-dimensional sample picture

coordinates to their three-dimensional equivalents. This provided a configuration Eile for

use in the client computer.

 Once the rendering system was receiving correct tracking values from the straps

system, these values needed to be appropriately mapped to the digital characters