Game Development Reference
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identical or slightly different. This means that for a screen viewed from a distance
d o , it should be equal to the product of the focal length f by the enlargement M of
the object: d o =
f
·
M.
C3 The distance of the main object observed with respect to the cameras should
be equal to the distance of its image with respect to the observer.
These conditions are used in a specific case of visual telepresence in the following
section.
13.1.3 Creation of 3D images for teleoperation
13.1.3.1 Stereoscopic visual telepresence
We will now present a teleoperation application in stereoscopic vision developed at the
Direction des Etudes et Recherches of EDF in partnership with our Robotics research
centre at the Ecole des Mines de Paris. The overall objective is to study the benefits of
the techniques of Virtual Reality for Teleoperation.
Teleoperation works in nuclear stations can be improved by stereoscopic visual
telepresence. Teleoperation works involve implementing tools, using controls, carrying
out weld re-filling, etc. in a distant and often hostile environment. It is necessary to
make the operators telepresent in the work environment by providing pertinent and
realistic information. This information comes from video camera images and computer
generated images obtained from models. Today, we are in a phase where the two
sources are often used separately with their fusion being only an experimental field.
The practical case involves a series of teleoperation tasks in a water box of a steam
generator (confined space of a quarter of a sphere of 3.5m radius). The objective aimed
at is a better visual immersion of the operator in the work space. In all the cases, the
teleoperator should always be capable of easily placing himself with respect to the task
he accomplishes.
We use two techniques for three-dimensional vision. Their principle is based on a
temporal separation of two images for the two eyes with a double frequency (100Hz)
stereoscopic screen in order to retain 25 images per second for each eye. The separation
is done either by circular polarisation of light and its screening by passive goggles, or by
electronic blocking of images for active goggles with liquid crystals. An electromagnetic
localisation sensor enables determining the 6 degrees of freedom of the operator's head
at a frequency of 120 measurements per second. This sensor enables controlling the
movements of cameras with respect to the head movements (Figure 13.10).
13.1.3.2 Study of stereoscopic vision
The fusion of images displayed on a screen cannot be done without visual strain except
under certain constraints, mainly:
The vergence-accommodation relation should be modified a bit to avoid visual
strain.
The horizontal parallax should be limited, but big enough to perceive the depth.
The vertical parallax should be zero or very limited.
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