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We have developed novel algorithms for the haptic display of shape, texture
and friction of solid surfaces using the PHANToM (Morgenbesser and Srinivasan,
1996). We have also performed psychophysical experiments to determine
the effectiveness of such rendering algorithms in conveying the desired
object properties to the human user. The results show that even when the
user is exploring nominally flat surfaces, he can be made to feel as if
he is interacting with a shaped and textured surface by appropriately
varying the direction of the force reflected back to the user. These new
algorithms, called "Force Shading," permit the mapping of a shape or texture
onto a polygon, so that they may be used in haptic rendering in the same
way that texture mapping and color shading are used in graphics rendering.
We have performed psychophysical experiments to determine the simplest
polyhedral representation that is acceptable to the user as a smooth continuous
surface. The PHANToM, which is a high performance haptic interface device
developed as a part of the VETT project, was utilized for the experiments.
It is capable of reflecting back 3-dimensional force vectors within a
3-dimensional workspace. In the first set of experiments, in each trial,
the user is asked to stroke the stylus of the PHANToM over a continuous
cylindrical surface and a polyhedral approximation to it (both are virtual
surfaces). The polyhedral surface is associated with a force-shading scheme
such that the subject can vary the effective average curvature of the
polyhedral surface. The subject is asked to modify the force-shaded polyhedron
until it perceptually matches the feel of the continuum surface. These
experiments have been conducted for polyhedra with one to three faces
approximating cylinders of several radii of curvature. The results show
that the force-shading algorithm is successful in creating the illusion
of a continuous surface and that the polyhedral surface needs to have
a higher average curvature than that of the continuous cylinder that is
its perceptual equivalent.
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the second set of experiments, subjects manually explored the haptic display
of various virtual polyhedral approximations of a circular cylindrical
bump, with or without force shading. They then indicated the perceived
shape by selecting one from a menu of shapes displayed on a computer monitor.
Without force shading, the subjects accurately identified the polyhedral
nature of the virtual bumps. With force shading, however, the subjects
identified the polyhedral approximations as feeling closer to that of
a smooth cylinder. The higher the number of polygons, the higher was the
percentage of trials in which the shape was identified with a smooth cylinder.
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results from both the experiments imply that the same polyhedral approximations
to object shape used in visual displays can be used for haptic displays
as well, provided the haptic renderer does the appropriate force-shading
to make it feel continuous and smooth. Therefore one can envision a data
architecture for multimodal VEs where the core geometric information about
object shapes relevant for the specific virtual environment of interest
is independent of visual or haptic display modalities.
Click here to read more about HaptiC-Binder.
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