Game Development Reference
in case of semi-cylindrical screens, rear projection is quite rare and certainly more
difficult. It is easier if the bend radius is large enough.
Generally, these installations are used to show a virtual scene on a large scale.
For applications requiring an accurate life-sized representation of objects, a visiocube
or immersive desk type of configuration is to be preferred. The advantage of large
screens is that several users, generally a few dozens, can together watch scenes of
computer-generated 3D images in real time. These installations are used especially for
collaborative project review or visualisation of scientific data. They provide a visual
media which helps taking decisions regarding the construction of a project on the basis
of its virtual model. For example, the observers can walk through a vast architectural
complex, like in the real world, as the images displayed are life-sized.
As a result, it is impossible to provide for a system tracking the point of view
of all the users simultaneously. The image is thus calculated and is exact only for a
single user, generally the observer sitting at the centre, and the other observers get
an approximate and slightly deformed image of the virtual scene. But considering
the accuracy of display of these systems, this defect is generally not troublesome and
sometimes is not even perceived. A flat screen proves to be more suitable than a curved
screen for certain scenes. For example, in the classic case of a vehicle representation,
where a flat screen starting from ground level is a better option.
The visiocubes, or CAVE 2 , are probably the most widely-known solutions using large-
screen projection. They are also the most expensive and the most difficult to set up and
maintain. They are in the form of a cube-shaped room of about three meters of arris.
Stereoscopic images of the virtual world are projected on a number of surfaces
ranging from four (three walls and the ground) to six for certain configurations. This
configuration creates a good sensation of immersion thanks to the layout of screens
which gives the user a large field of vision, the stereoscopic visualisation and the display
shown according to the head movements captured. Tracking the head helps calculating
the images to be projected on the screens as per the user's position, which in turn helps
to continuously match his point of view with the camera in the virtual environment.
By turning around an object, the user can change his point of view and examine it from
any angle. These visiocubes can accommodate several persons, up to three or four, at
the same time. However, in this case it is necessary to provide a tracking system for
each user (read paragraph 188.8.131.52). This type of systemmakes it possible to immerse a
user in an environment of his size. The visiocubes generally use one (active stereoscopy)
or two (passive stereoscopy) projector(s) per screen, but there is no harm in increasing
their number to improve the image resolution (read paragraph 184.108.40.206). Except for
the ground screen in a system without roof that will have a direct projection display,
the images will generally be displayed on the screens by rear projection. If we want
rear projection on the ground (to avoid creating the user's shadows), a transparent
and sturdy screen would be required to bear the weight of a number of persons (a
very expensive solution). The first visiocube, the CAVE (Cruz-Neira et al., 1993), was
2 A name commonly used to refer to systems based on large-screen projection, in reference to
the first such device created, read further.