Game Development Reference
scene from inside a vehicle). So as not to disturb the movements of the head, the head-
mounted displays need to be symmetrical, as light-weight as possible and should have
a centre of gravity towards the front of the head so as to take support of the dorsal
muscles of the neck that are stronger and less prone to fatigue. Statistics on this subject
are available, but they focus primarily on the dynamic parameters, as they concern the
study of the resistance of a pilot wearing a helmet in flight.
If we want to study all these problems and characteristics of the quality of a head-
mounted display as a visual interface, asking the user whether he can see the images is
not enough unless we can make do simply with an “eye-catching'' demonstration (an
appropriate name). We have offered a number of tests related to the professional use
of a head-mounted display. It is necessary to validate the sensorimotor immersion and
interaction (I 2 ) before studying cognitive and functional I 2 .
For location of the head-mounted display, the two major problems are:
Is the accuracy of location of the head sufficient for the application?
Is the latency time taken by the sensor and the creation of images acceptable?
For vision, the two major problems are:
the compatibility of the visual fields in the head-mounted display in the virtual
environment with the visual fields used in reality (horizontal, vertical and
usefulness, validity and constraints of stereoscopic vision for the application
(read the chapter “stereoscopic restitution of vision'').
11.3.5 Video eyeglasses
22.214.171.124 Video-eyeglasses with LCD screen
Video-eyeglasses are slightly different than head-mounted displays because they make
it possible to see virtual images while not being completely cut off from the external
world. The visual field is not completely blocked by the optical device and the observer
can see the sides of his external environment. As a result, the user perceives images on
a virtual screen, as though floating in the air, with a less convincing visual immersion.
The video-eyeglasses compare with head-mounted displays if they can be equipped
with a tracker. In this case, the main advantage is that the person is not completely
cut off from the external world for functional reasons related to the application or
for ergonomic reasons: less risk of dizziness, lighter and more bearable device. Less
effective visual immersion is, however, its disadvantage.
11.3.6 Head-mounted display and semi-transparent device
Head-mounted displays with semi-transparent screens are also available. They super-
impose computer generated images on the view of the real world (See-through HMD
or display device for helmet). These devices, some of which are relatively heavy, were
designed for certain applications like simultaneous display of dashboards and the exter-
nal view for airplane pilots (Chung et al., 1989). Whatever be the interface, it uses a
semi-reflective screen which receives one or more images, which superimpose the nor-
mal human vision. The screen principle is used in the “old'' fighter aircrafts in the form
of a small inclined screen on which the information necessary for steering are displayed.