Game Development Reference
In-Depth Information
a pull-down menu, symbolically commanding a door to open, etc. In the second case,
the trackers can be replaced with standard command interfaces (joysticks, 3D mice,
etc.).
They, when placed on a table, help the user to manually control the movement
of a cursor thanks to the relative movements of the interface with respect to a neutral
position. The distance covered by these movements is very small (a few millimetres to
a few centimetres). The command interfaces thus do not involve locating the hand in
a space and are evidently based on principles other than trackers. It should be noted
that in case of a tracker the cursor movement should be natural, i.e. without too much
mental effort. Unlike the 3D mouse and joysticks with which the users, except those
who are used to this type of interfaces, move the cursor manually, with some thought
and in a less natural manner. Though a tracker can be used in 3D cursors, joysticks
and 3D mice cannot be used in sensors locating the user's hand.
As trackers have already been presented, the chapter is thus divided into two main
sections: first datagloves, and then the different command interfaces. The command
interfaces are presented in this chapter, but are to be compared with the trackers, in
the case of command actions in the virtual world.
7.2 DATA GLOVES
Data gloves (or “digital gloves'') help to measure the relative movements of the fingers
with respect to the hand. It is also necessary to mark the position of the hand with a
tracker to fully determine the absolute movements. The types of trackers used for this
function are mainly electromagnetic sensors and sometimes ultrasound sensors. The
main problem is measuring the rotations of the phalanxes of the fingers with devices
that are light and less bulky. There are several competing principles: measurement by
fibre optic deformation, by Hall effect or by resistance variation. The main technical
problems faced with these devices are repeatability, precision and reliability of the
devices.
7.2.1 Fibre optic gloves
This was the first principle used for a glove, which was designed by the American
company VPL, a pioneer in the field of virtual reality: the famous fibre optic DataGlove,
invented by Thomas Zimmerman in 1987, which is not marketed any more. Two (or
three) optical fibres are attached to each finger of the glove. These are aligned with
the fingers and are more or less long to detect the movements at different articulations
(Figure 7.1).
The optical fibres are connected to an optoelectronic device. One of the ends of
each fibre-optic loop is connected to an LED and the other end is connected to a
phototransistor. As the fibre is straight, there is no reduction of the transmitted light.
On the other hand, if the fibre is bent, the luminous intensity received is lessened
because the conditions of perfect reflection no longer exist and the light received is
reduced. The optical fibre is bent to increase the loss of light when the cable is bent.
The variation of intensity of the light reflected by the fibre is a function of the articular
angle, which helps to deduce its value from it. The relation between intensity and angle
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