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previously, the recent emergence of graphic - gestural selection hybrid solutions (see
the TULIP and C 3 solutions described before). The benefit of these methods is to take
advantage of each of the two methods in proposing two modes of selection: a novice
method that places emphasis on the graphic menu, and an expert blind mode that
makes quick gestural selection possible (similar to keyboard shortcuts in 2D).
The selection and use of physical tools is an approach conceptually similar to using
virtual tools but, instead of being proposed in a virtual form, the tools are proposed in
the form of accessories (or “props'' in English). The act of holding a physical object in
the hand gives a kind of “passive haptic feedback'' to the surface gripping the object,
which makes a more intuitive usage possible depending on the role of the tool. One of
the most significant examples of using tools is the application in neurosurgery proposed
by Hinckley et al. (1994). In this application, the general practitioner has many tools
for visualising and manipulating his model (doll's head for manipulation of the brain
and glass plate for positioning the cutting plane).
The last alternative consists of using a hardware interface dedicated to application
control. Two main approaches can be cited:
the button is a selection mode widely used in 2D thanks to keyboard touch pads or
mouse buttons. Unfortunately, portability constraints that generally predominate
in a virtual environment do not very often permit having hardware interfaces with
many keys. The most current hardware interfaces generally have a limited number
of buttons (for example, a single one for the stylus of the Polhemus Fastrack
system). We can however find some options that are more or less bulky andmore or
less portable. In this case, the selection of a command is equivalent to an operation
of the “keyboard shortcuts'',
PDA (palmtop computer) can be used as the control hardware interface. It gives
unparalleled computing power and flexibility and communicates with the host
computer through infrared. Watsen et al. (1999) for example, use a PalmPilot in
a visiocube.
The aim of Tangible Augmented Reality is to reduce the separation between the virtual
world and the real world (Billighurst, 2001). For this, each virtual object is associated
with a real object that allows controlling it. The user interacts with the virtual objects
by manipulating the corresponding real objects (tangible). For example, a file can be
used like a menu in which the user arranges a series of physically empty sheets, but
virtually associated with certain content.
Pangaro et al. (2003) proposed a rather unusual magnetic peripheral with force
feedback. The Actuated Workbench is a tool that uses magnetic force to move objects
on a table, in order to provide a feedback to the user. The functions of research,
sorting, cancelling/redoing, highlighting and guiding the user interventions are among
the possible uses.
Beyond the classification of application control interfaces proposed above, the
existence of hybrid solutions using many of the concepts presented is to be noted. For
example, we think of multimodal solutions like TULIP or C3, where speech, gesture
and/or graphics coexist. The existing solutions are not completely satisfactory and
are often less effective than 2D solutions in several aspects: slower selection, more
frequent errors, difficulty when there are many choices (commands), greater cognitive
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