Biomedical Engineering Reference
In-Depth Information
•
Virtual walking speed should stay relatively constant during the rhythmic phase
to avoid detectable variations in optic flow—the change in patterns of light on the
retina occurring during movement.
•
The system should allow fine positioning or maneuvering steps that do not initiate
a full step's movement.
Goals for setting direction
. The goals for direction setting are to make it as easy as
natural walking and to avoid introducing sensory conflict.
•
Users should be able to move in any direction—forward, backward, sideways, or
at any angle.
•
As in natural walking, the direction of movement should be independent of user's
view direction and body orientation. Reinforcing the results reported in Bowman
et al. [
3
], the description of the
Pointman
interface includes a cogent argument for
independence of these parameters for tactical movements [
37
].
•
Direction setting should be hands-free, as it is in natural walking, so the hands can
be used for application-specific interactions with the environment.
11.2 Walking-in-Place Interfaces
Walking-in-place (WIP) is a locomotion interface technique for Immersive Virtual
Environment systems that uses data describing the stepping-in-place gesture to con-
trol locomotion speed and uses any one of a number of techniques or input devices
to set locomotion direction.
11.2.1 Setting Speed: Interpreting Stepping Gestures
Repeated stepping gestures have several distinct, observable, and measurable phases.
Starting from the eight-phase human gait cycle, [
41
] proposed the six-phase walking-
in-place gait cycle shown in Fig.
11.2
. There are three events associated with each
leg's step: foot off, maximum step height, and foot strike. With appropriate sensors, it
is possible to detect each of these events, make measurements about them, and apply
time stamps to them. The resulting data are what is available to determine whether
the user is moving, and, if she is moving, how fast. The question of whether the user
is moving includes both whether the user is starting to move and whether the user is
stopping.
11.2.1.1 Detecting Foot-Strike Events
The earliest WIP interfaces computed forward motion based on indirect or direct
detection of foot-strikes: each time a foot strike was detected, the user's viewpoint
