Biomedical Engineering Reference
In-Depth Information
Having explained the roles of coordinate systems, we can see that short-range
physical movements are captured in the movements of the Head Tracker and Hand
Tracker relative to the Display Center.
For virtual travel over longer distances, the position of the Display Center can
be moved relative to the World coordinates. There are many options here. Funda-
mentally they involves changing the transformation of the Display Center relative to
the World origin. This might involve translation, rotation and scale of the Display
Center. However, it is very common for certain restrictions to be set. For example,
there might be translation only: if the person is surrounded by the display system,
they can simply physically turn to see any direction, whereas in a typical SSD with
three walls there will need to be a rotation metaphor. If there is translation, then it
might be 2D only (i.e., on a plane), or use some form of surface-following algorithm
so that the user is always at the same height above the ground. Other questions must
be answered as well. If there is translation, in which direction should it be? If there
is rotation or scaling, around which point should the scale or rotation occur (e.g.,
the Display Center, the User Ground Center, or the Head)? And how does the user
indicate how to start and stop traveling?
A task decomposition for travel techniques is provided by Bowman et al. [
2
]. Their
decomposition, which is shown in Fig.
7.20
, decomposes the travel task into different
sub-tasks: start to move, indicate position, indicate orientation, stop moving. To start
to move, the user might press and hold a button, and to stop moving she might release
Start To Move
Specify Position
discrete target specification
(select object in environment,
select from list, position 3D
cursor, automatic selection,...)
one time route specification
(set series of markers, specify
curvature and distance,...)
continuous specification
(gaze directed, pointing,
physical steering props, virtual
controls, 2D pointing, ...)
Travel
Indicate Position
Specify Velocity
Specify Acceleration
Indicate Orientation
Stop Moving
Fig. 7.20
Taxonomy of travel techniques focusing on level of user control [
2
]
