Biomedical Engineering Reference
In-Depth Information
To be cost effective, walking-in-place techniques have often made do with very little
information about the user's actual motion. In some cases, the only data available for
use in the locomotion algorithm is from the head tracker. Full body tracking systems
provide rich data, but also are costly, encumbering, and inconvenient. Their use has
to be carefully balanced against the improvements in naturalness made possible by
the richer data.
Consumer products have started to change the landscape. Applications for the
Kinect™ range camera can compute and update the 3D pose of a user's skeleton
each frame time. The Kinect is inexpensive and does not require the user to wear any
additional gear [ 46 ]. Small wireless sensors—accelerometers, magnetometers, and
gyros—will be an inexpensive and non-encumbering source of data measuring user
motion that can be used as inputs to the locomotion algorithm. A proof-of-concept
system using such devices is described in Kim et al. [ 16 ].
With a richer set of input data, walking-in-place locomotion techniques will be better
able tomodel and simulate the experience of natural walking for users of IVE systems.
11.3 Real-Walking Interfaces
Real-walking interfaces enable HMD-IVE-system users to naturally walk around the
virtual scene just as they would in the real world. Because the user must be tracked,
restricting the size of the virtual scene to the size of the tracked space is the simplest
case for real-walking. If the virtual scene fits in the tracked space, the user can freely
walk about in the entire virtual space, the user's real-world speed can be mapped in
a one-to-one ratio to her virtual speed, and her direction in the virtual scene can be
directly controlled by her direction of motion in the real world.
Complications with real-walking interfaces arise when the virtual scene is larger than
the tracked lab area. Mapping the user's actual speed and direction one-to-one with
virtual speed and direction no longer enables the user to travel through the entire
scene, as to do so would require leaving the tracked area. Numerous techniques,
most of which exploit the imprecision of human perception, have been developed to
make real-walking a viable locomotion technique for larger-than-tracked-space vir-
tual scenes. Initial implementations focused on transformations of the scene model or
the user's motion by manipulating the ratio between the user's real and virtual speeds
and directions. A newer technique changes the structure of the scene model [ 34 ]. We
discuss both approaches.
11.3.1 Manipulating Speed
Manipulating speed in real-walking interfaces can be thought of as altering the ra-
tio between the user's real walking speed and virtual speed so that it is no longer
one-to-one.
 
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