Game Development Reference
In-Depth Information
It is thanks to the boom in virtual reality that the most sophisticated location
sensors were devised. These trackers are often used in virtual reality system to:
locate the head of the user wearing a head-mounted display;
locate (6 degrees of freedom) the hand with data gloves;
measure the spatial movement of the tip of the hand that helps handling a virtual
object or controlling a cursor naturally in a virtual environment;
locate a body part, for example in “motion capture'' (location of the entire body)
which we will discuss in the next chapter: Special interfaces used to locate the body.
A good spatial location sensor normally determines the 6 parameters connected to the
6 degrees of freedom. However some sensors measure only three parameters:
The 3 coordinates of the object's translation motion with respect to the reference
The 3 coordinates of the object's rotation;
The 3 coordinates of locating an object on a plane.
This chapter deals with spatial location sensors. We will not talk about simple dis-
tance measurement or angular orientation sensors even though by using a device that
uses this type of sensors it is possible to determine the spatial position of an object
by measuring various points of this object with respect to the reference point (trian-
gulation method). Similarly, we will not study the “navigation'' sensors of terrestrial
geo-location used in fields like mobile robotics, aeronautics and also recently used in
external applications using augmented reality. We will thus concentrate on only the
sensors that locate an object in a restricted area, such as the area around a computer
or a part (a few centimetres to a few decametres). We will also exclude the manual
sensorimotor interfaces with force feedback, all of which compulsorily measure the
hand position when they apply the feedback forces on the hand (refer to the chap-
ter covering these interfaces). In this type of force feedback interfaces, the position
measurements are generally based on the principle used in mechanical trackers that
measure distances, described further.
6.1.2 Location sensor and command interface
As we mentioned earlier, a tracker can be used to handle a virtual object or to control a
cursor in a virtual environment. In the first case, the user acts “naturally'' in the virtual
world because the tracker only follows the hand movement. While in the second case,
the user generally has to control a specific action: for example, moving in the virtual
world by indicating a direction, pointing at a dropdown menu, symbolically open a
door, etc. In the second case, the usual command interfaces (joysticks and 3D mouse)
can be used instead of trackers. Using these interfaces, generally placed on a table,
the user can manually command 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.
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