Biomedical Engineering Reference
In-Depth Information
Fig. 7.8
A later version of the touring machine system. Courtesy of Steve Feiner, Columbia
University
just in the direction of travel, but up and down. All of these, and many other subtle
effects, need to be recreated in VEs if a purely natural walking interface is desired.
In the virtual reality model discussed previously, the concept is that the system
tracks the body and recreates the perceptual cues in a structure that is analogous to
the real world. In practice this means that the system tracks the head of the user and
uses this to orient a pair of virtual cameras, one for the left eye and one for the right
eye. It would be ideal to track the eyes as well, both direction and focus, and then
adapt to that, but that is beyond the current state of the art.
Since it is not possible to track the user in an unlimited area, interaction devices
must be used to provide control input to effect the two tasks we identified above.
While we will discuss the actual interaction tasks in the next section, it is worth
pointing out the degrees of freedom that are required. The task of placing a camera
in the world involves six degrees of freedom (DoF): three for orientation and three
for translation. For two eyes, two cameras are required, but typically these are rigidly
attached to the head, so a single six-DoF position/orientation needs to be calculated.
In one extreme, say the desktop display type from Table
7.1
, nothing about the user's
