Game Development Reference
Figure 6.7 ART system. (Illustration: A.R.T. GmbH, with permission)
Figure 6.8 Diagram of a three camera system demonstrating the problem of intersection of visual
parameters related to the tracker depend on the relative position of the cameras and
therefore, must be calculated each time you install the systemon the site. This operation
generally involves scanning a mechanical structure identified in the field of the cameras
for about one minute (“the wand dance'').
For example, the structure can be a beam of about one meter on which the targets
are fixed. The calibration program calculates the extrinsic parameters. The inputs
of this calculation are the images obtained during the “wand dance'' as well as its
knowledge of the three-dimensional position of targets on the beam.
Other systems are based on the same principle, but with a rigid structure between
the two cameras. North Digital proposes the POLARIS system. The procedure of
calibration of the extrinsic parameters is carried out in factory.