Biomedical Engineering Reference
In-Depth Information
by an eye-tracker, direction of the torso, the relative direction of hand from eye or
the relative position of the two hands. All of these have been implemented in VE
systems. Pointing with a hand tracker is a very commonly implemented technique
because it decouples head orientation from travel so that users can look around while
moving [
2
].
7.4.3 Indirect Self Motion Control Techniques
Indirect control techniques set the target of travel in an indirect or asynchronous
manner. The most common technique is to indicate a target in the environment,
and then to enable travel to that position over a period of time or instantly (when
it is known as teleporting). Indicating the target might involve simply targeting an
object by pointing directly (e.g., “go over there”), or on a map or miniature world.
An example of the former is the ZoomBack technique [
47
] that uses a typical ray-
casting metaphor to select an object in the environment, and then moves the user
to a position directly in front of this object. Ray-casting has been used in other
3D interfaces for target-based travel as well, e.g., [
3
]. An example of the latter is the
previously mentioned WIM technique [
26
], in which a small human figure represents
the user's position and orientation in the miniature world. The user places the user
representation in the WIM, and then a path is calculated that moves the camera to
this location, taking into account any rotation that is necessary to reach the target
orientation. In this technique the transition could be achieved by zooming in to the
WIM itself, or it could be planned as a motion through the VE at the original scale.
7.4.4 Scene Motion Techniques
A common alternative to self-motion travel is to manipulate the scene. This is very
common on desktop interfaces where the metaphor is that the camera is static and
the object on the screen is moving. Less obvious is that this can be turned in to a
travel technique, in that the object is considered stationary and the camera is moved
around the object. The rotations of the camera for an immersive system would be
violent, so this is not very commonly done, but the translation equivalent (pull and
push objects) has been demonstrated. Most notable is the “grab the air” technique
[
19
,
40
]. In this technique the user can grab anywhere in the environment and when
they move her hand back and forth, they move themselves through the environment.
This motion can be scaled by using two hands. Similar techniques include Mine's
Scaled-World Grab technique [
24
] and the LaserGrab technique of Zeleznik et al.
[
47
]. A related set of techniques involve manipulation of objects using image plane
techniques [
28
].
