Game Development Reference
In-Depth Information
down their movements and to acquire precision. Depending on the speed of the hand,
PRISM determines in which real hand - virtual object correspondence mode it should
function. A slow movement defines a desire for precision, unlike a rapid movement,
for which the virtual object should follow the hand. The gap created between these two
positions, i.e. real hand and virtual object is made up for during the acceleration phases
of the hand that no longer looks for precision, or by a simple movement in the oppo-
site direction. By associating this behaviour with each axis of a reference point aligned
with the direction of the main movement, a user can move quickly with reference to a
main axis without drifting with reference to the secondary perpendicular axes.
12.5.3.2 Rotation of a virtual object
The centre of rotation is one of the main differences between all manipulation tech-
niques which the user can use. Hand-centred rotation (which means that the hand is
the centre point of all objects) is the method most used, because it is directly related
to manipulation of objects in the real world. In certain cases, however, it is desirable
to have a centre of rotation based on an object that lets the user stand back and have
a good perspective of the modification. When the centre of rotation is determined,
we should be able to indicate the angle or angles of rotation. There are mainly two
schools: one that prefers quick and less precise rotation and the other that prefers
precise rotation. Quick rotation makes it possible to give an approximate orientation
of an object, for example, by indicating the angle of inclination with the hand. It is
useful in conceiving, for example, a rapid prototype, without special constraints and
to obtain an overall view. On the other hand, precise rotation matches other expec-
tations. For example, a surveyor wishes to precisely position an object in relation to
another so that his entire creation could be functional.
Hinckley and his colleagues (1997) studied several rotation techniques (rotation
on a virtual sphere, Arcball), and demonstrated that peripherals with several degrees
of freedom are much faster (
+
36% in relation to using a 2D mouse) and do not
compromise on accuracy at least in terms of orientation.
12.5.3.3 Conclusion
In parallel to the development of new interaction techniques, a significant effort has
been taken by the community in recent years on the research and implementation of
more rigorous assessment methods for comparing and characterising the performances
of these techniques.
12.6 APPLICATION CONTROL ANDTEXT INPUT
12.6.1 Application control
Issuing commands with the aim of changing, for example, the system status or the
interaction mode, as well as editing of parameters, is classified under the term “appli-
cation control''. In the 2D world (workstation with monitor, keyboard, mouse), an
interface has quickly become popular. Commonly referred to using the term WIMP
(Windows, Icons, Menus, and Pointing), it designates the classic Windows system,
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