Game Development Reference
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the different axes of the selected reference point after which each projection is sent to
the corresponding joystick.
By virtue of its characteristics, DigiHaptic is predisposed to fine manipulations,
and is also well adapted to the navigation with change of the point of view of the
camera. In this case, each degree of freedom is used in elastic mode for a speed control
of the movements of the camera. The thumb and the ring finger are used to orient
the camera and the index finger moves it. The selection of a switch helps to pass into
translation mode to control the horizontal and vertical movements of the camera in its
reference point. Irrespective of the mode used, a force feedback is sent on each joystick
(thus on each finger) when one encounters problems with the camera 2 (Casiez et al.,
2003b).
7.3.3 Six degrees of freedom command interface
for a large screen
The CAT (Control Action Table) is an interface that has been developed in LaBRI, a
research centre in Bordeaux, to make it possible for several users to easily interact with
a virtual environment displayed on a large screen, like those of the immersive rooms.
The CAT resembles a coffee table whose platform can be oriented in space. Sensors
recover the orientation of the platform and the forces applied on it. Thus, the CAT is a
6 degrees of freedom interface, mixing the isotonic and isometric resistance modes: the
rotations to be applied in the VE directly come from the orientation of the platform
while the translations are proportional to the quantity of forces applied on the latter
(Figure 7.13).
The CAT was initially designed to facilitate manipulation of 3D scenes. The user
holds in his hands the scene that he is viewing, using the platform. Identical orientation
of the scene and platform facilitates an intuitive interaction. The CAT can also be used
as a 3D steering wheel to navigate in VE. The 6 DOF can be manipulated simultane-
ously or separately depending on whether you want to make complex paths or paths
involving only a small number of DOF. Moreover, the CAT platform is equipped with
a graphics tablet that facilitates 2D interaction. The user places a representation of the
platform in the virtual space and then moves a cursor on this platform by moving a
stylus on the physical platform of the CAT.
The addition of a 2D constraint in the 3D virtual space helps to carry out selection
tasks as well as handling tasks with precision. This also facilitates effective use of the
2D menus in 3D space to control the system, while remaining immersed in the VE. The
platform remains stable when released and thus involves no modification in the VE.
These features facilitate collective use of the CAT. It can be used with reduced fatigue
and is not limited by anatomical considerations. The CAT is versatile and effective as a
command interface for the applications of virtual reality 3 . A desktop version based on
the principle of separation of the CAT (isotonic rotations/isometric translations) has
been developed by the Immersion company, in collaboration with LaBRI (Figure 7.14)
(Hachet et al., 2003).
2 This paragraph was contributed by G. Casier.
3 This paragraph was contributed by Martin Hachet.
 
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