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Figure 13.15 Diagram showing the virtual position of the dashboard, seen in 3D
13.2 EVALUATION OF STEREOSCOPICTECHNIQUES
13.2.1 Advantages of stereoscopic vision
Researches were undertaken to quantify the contributions of stereoscopic vision for
a user. The studies were specifically focused on vision systems with a screen, since
head-mounted displays are still very new. The main researches focus on improv-
ing the perception of depth due to stereoscopic vision, the additional visual strain
and problems inherent to stereoscopic vision (crosstalk, fusion, etc). Research by
Tetsuya Mityashita (Tetsuya & Tatsuo, 1990) focuses on the causes of fatigue
and the possible improvements for reducing it. Visual strain is lower for a large
depth of field. It is only slightly higher for a vision with disparity compared to a
vision without disparity (the experiment was performed with two miniature cathodic
screens).
13.2.2 Choice of parameters of stereoscopic vision
As we have mentioned previously, the parallax should be small so as not to create big
difficulties for stereoscopic vision. In other cases, the brain either cannot merge the
two images or it does it with a certain strain. The aim is therefore to create stereoscopic
images with low parallax while maintaining an effect of depth, and not disturbing the
relation between vergence and accommodation too much. If possible, the main object
viewed has to be positioned close to the plane of the screen.
With reference to experimental studies (Valyus, 1962), the difficulty of merging
two plane images with a parallax angle greater than 1.5 degrees was proven. The limit-
ing parameter is the parallax angle (angle of vision for two homologous points) and not
the parallax distance. Our studies undertaken within the framework of teleoperation
with real images indicate a limit of 1.2 of the parallax angle (Fuchs et al., 1995).
The study done by Yei-Yu Yeh (Yeh & Silverstein, 1990) examines the limit of
fusion and the estimation of depth. The limit of merging is analysed on the basis of
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