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selection-manipulation of objects and control of applications. The current main inter-
action techniques for these three tasks have been described, analysed and discussed.
Tasks are most often performed in an intuitive and direct manner by the user: by
hand, but also with the help of other motor interfaces like the direction of vision or
speech. Interaction can also use sensory interfaces other than vision like haptic feedback
(force and tactile feedback) or audio feedback. Haptic feedback is not considered in this
chapter as it is dealt with elsewhere. The same applies for audio interactions (sound,
speech). For a much more detailed review of 3D interaction, also see Bowman et al.
(2004) where an entire book has been devoted to this subject.
12.2 VIRTUAL BEHAVIOURAL PRIMITIVES OF OBSERVATION
12.2.1 Classification
As we have just pointed out, the “observation'' VBPs are different according to the
human senses put into play for observation of the environment. The senses are chosen
offhand at the functional I 2 level. There are therefore three sub-VBPs of “observation'':
visual observation, auditory observation and tactile observation. We could also talk
about kinaesthetic and proprioceptive observation, but generally these are only sub-
tasks depending on “action or “movement'' VBPs. As a result, they have not been
considered in this section. But the reader can always find counterexamples: when he
goes to the market, he weighs the melon to observe its maturity. The three sub-VBPs
of “observation'' can be brought together by the combination of senses.
It can also be studied and determined at the functional I 2 level whether the aim of
observation is to move in space, to understand the virtual environment or to search
something or someone in this environment. We must ask ourselves the question to
know whether it is necessary to mentally rebuild the tridimensional (3D) space. Should
the user save all the space visited or only the one where he finds himself? Wouldn't
a reconstruction of the bidimensional (2D) layout of the space suffice? For example,
even on a hilly terrain, the observer makes an offhand bidimensional representation of
it. On the other hand, for a multi-storey building, the representation is tridimensional,
even if it is often an extension of a bidimensional representation and referenced to the
vertical of the place (in a space station, this procedure must be less easy).
The number of simultaneous observers is a criterion that should be taken into
account as there are only some visual interfaces that are multi-users. Metric and angular
dimensions of the space observed are to be determined because they directly influence
the choice of the behavioural interface.
12.2.2 Visual observation
A visual observation is done on different spatial zones. We have classified them into
four categories, but there is a continuum among these cases. The spatial zones of
observation do not take into account the VBPs of movement that can increase the
zone of observation. It is, therefore, with the restriction of a stationary observer in the
virtual environment that the main solutions are studied:
the viewpoint is fixed, thus limiting the field of vision to a sufficiently narrow
conical area;
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