Game Development Reference
In-Depth Information
to take into account the gaps between the actual position of the eyes and the position
of the tracker fixed on the pair of eyeglasses.
Though this gap varies from user to user (the pair of eyeglasses is worn differently
by each user), it is often possible to consider an “average'' gap, by considering that the
point tracked is located exactly between the two eyes and the average inter-ocular dis-
tance is 6.5 cm. Alternatively, the two optical centres of the eyes can be determined by
individual calibration by asking each user to point with each eye the targets displayed
on the screen through a tracked tube. The intersection of the targeted lines is located
at the optical centre of the eye. In case of a 3D environment, the user can use a virtual
cursor to visually point out the different locations of a real object in front of the screen
when the object's exact position is known (with respect to the screen). Other similar
methods are also possible. It goes without saying that not only the point of view, but
any other tracked element (hands, other accessories, etc.) should also fulfil the same
calibration conditions.
Calculation of an image
Once the position of the user's eyes is known, it is possible to calculate the image to
be displayed accordingly.
For this purpose, it is necessary to provide the software with an accurate represen-
tation of the screen configuration (format and size) in the reference of the 3D graphic
environment.
Unlike a traditional application based on a single computer screen and thus gener-
ally without a head tracker, calculating the image for an immersive environment will,
in most of the cases, require the use of an asymmetric frustum. As this frustum is
defined by the position of the user's eyes as well as the internal representation of each
screen in the software, this model has to be as accurate as possible.
Projection of an image
Obtaining a projected image that is compliant, in terms of geometry and colours, to
the theoretical image calculated in the previous step is an extremely difficult task. Sev-
eral factors are likely to affect the image rendered: relative position of projector and
screen, projector setting, physical characteristics of the screen, etc. There are so many
parameters that it is imperative to control them in order to obtain a display of optimal
quality. Firstly, the quality of the relative position between the projector, the possible
mirrors and the screen should not be neglected. Setting this relative position is partic-
ularly difficult when the screen is attached to the projector and the mirrors, if any. In
this case, since the screens are generally fixed, it is necessary to provide for a system
and a procedure for adjusting the position and orientation of the projector and the
mirrors. Once the projectors are correctly positioned, they can be adjusted accurately.
In the event of the overlapping of two contiguous images, the overlapping zones of
the images must be imperceptible so that the observer sees only a single image. For
this purpose, the edge-blending setting of the projectors must be finely tuned. Barco
offers solutions for real-time tuning of the edge-blending parameter (Optical Blend-
ing). Three cameras are placed in each projector in order to continuously adjust the
settings. On the other hand, the projector needs to be adjusted to display square pixels
in order to obtain images of the same resolution in all directions (image isotropy). Since