Game Development Reference
In-Depth Information
Similarly:
r B w
b 0
b 0
l
r C
r C =⇒
=
r C =
(3.3)
r B w
The formulae (1) and (2) define the maximum distance of discrimination of an object
situated at a distance r A before or r C after the plane situated at a distance r B .
The inverses 1/ r A and 1/ r C of discrimination distances represent the threshold of
stereoscopic discrimination in the case of an object located at a distance r A in front of
and at a distance r C behind the reference plane which itself is located at a distance r B
from the observer. The threshold of discrimination is defined as the average between
the two thresholds (in front and behind) and is given by:
1
r =
1
r B =
b 0
wr B =
=⇒
w ( r )
(3.4)
In this formula, b 0 is given in meters and w in radians. The unit in which w ( r )is
expressed is the inverse of metres. w ( r ) indicates the number of planes that can be
discriminated per metre in the direction of depth from a distance r (from the observer).
For example: If distance between the eyes is 65mm and the physiological threshold
is equal to 0.065 milliradians, the stereoscopic threshold will be equal to:
0 . 065
0 . 000065 ·
1
r 2
1000
r 2
(m 1 )
w ( r )
=
(3.5)
0.001 r 2 . This means that if an object is located at 10m from the
observer, he can see the relief only for two planes at 0.1m. For an object at 1m,
the relief can be perceived only for the planes separated by 1mm. To conclude, three-
dimensional vision is relatively efficient only for short distances. Since this vision causes
eyestrain, these considerations should force the designers not to automatically use
stereoscopic vision in any given situation, but only when it is justified to use it. We will
discuss this once again, but the reader should remember that stereoscopic vision, if not
used correctly, can go against the set goal: better perception of depth for an effective
visual immersion.
And hence r
=
3.2.3.4 Field of vision
Both the eyes take part in observing space. The area of space seen by either eye at a
single instant is defined as the field of vision. The points of space that are in the zone
of binocular overlap are seen simultaneously by the left and the right eye (in the head-
mounted displays) The characteristics of the field of vision for a stationary eye are
approximately 90 (temple side) and 50 (nose side) horizontally and 45 (up) and 70
(down) vertically. Let's not forget that the visual acuity is accurate only for a central
cone of 2 angle. When both the eyes are fixed, the overlap zone corresponds to the
binocular field of vision of approximately 100 in the horizontal direction.
If we want to achieve visual immersion, it is necessary to take into account the
movements of the eyes and the head. An eye can turn in its orbit by approximately
15 horizontally and vertically, with a maximum speed of about 600 /s. The head can