Stepping-Driven Locomotion Interfaces - Human Walking in Virtual Environments - page 252

11.3.3 Reorientation Techniques
Many of the locomotion techniques presented in Sects. 11.3.1.1 and 11.3.1.2 use a
reorientation technique (ROT) to handle the situation when large-area real-walking
techniques fail and the user is close to walking out of the tracked space (and possibly
into a wall or other obstruction). ROTs discourage the user from leaving the tracked
space and rotate the virtual scene around her current virtual location. This moves
the user's predicted next-path-direction into the tracked space. The user must also
reorient her body by physically turning in the real environment so she can follow
her desired path in the newly rotated virtual scene. Some techniques require the
user to stop; others do not. As a design goal, ROTs should interfere with the virtual
experience as little as possible.
In addition to waypoints, redirected walking [ 27 - 29 ] uses a ROT that employs a
loudspeaker in the virtual scene, played through user-worn headphones, that asks the
user to stop, turn her head back and forth, and then continue walking in the same
direction. During the head turning the virtual world can be undetectably rotated such
that the future virtual path lies within the real-world tracked space.
The ROT used in motion compression [ 19 , 33 ] is built into the motion compression
algorithm itself: as the user approaches the edge of the tracked space the arc of
minimum curvature grows quite small causing the scene rotation to be large. These
large rotations cause the user to feel that the scene is spinning around [ 19 ]. This
method does not require the user to stop.
In the method presented by Hodgson et al. when the user is about to leave the tracked
space the experimenter physically stops the user and physically turns the user back
into the tracked area [ 11 ]. The HMD visuals are frozen during the turn so that the
user can continue walking in the same virtual direction after the turn.
Williams et al. explored three resetting methods for manipulating the virtual scene
when the user nears the edge of the tracked space [ 43 ]. One technique involves
turning the HMD off, instructing the user to walk backwards to the middle of the lab,
and then turning the HMD back on. The user will then find herself in the same place
in the scene but will no longer be near the edge of the laboratory's tracked space.
The second technique turns the HMD off, asks the user to turn in place, and then
turns the HMD back on. The user will then find herself facing the same direction in
the virtual scene, but she is facing a different direction in the tracked space.
Preliminary research suggests that the most promising is a third technique that uses
an audio request for the user to stop and turn 360 ◦ [ 43 ]. The virtual scene rotates at
twice the speed of the user and stops rotating after a user turn of 180 ◦ . The user is
supposed to reorient herself by turning only 180 ◦ but should think she has turned
360 ◦ . This ROT attempts to trick the user into not noticing the extra rotation; however,
results from Peck et al. noticed that few participants were tricked into thinking they
turned 360 ◦ after only turning 180 ◦ [ 20 , 24 ].