Development and evaluation of a haptic rendering system for virtual design environments

This dissertation presents a haptic rendering system using a new data structure for shape representation, multi-resolution distance-gradient volumes, that addresses shortcomings of previous haptic rendering systems using polygonal meshes for shape representation. In an initial user study, I investigated the effect on sketching performance of different virtual reality (VR) components and parameter settings in the most popular commercial haptic rendering software, the General Haptic Open Software Toolkit (GHOST), which uses polygonal mesh models. The effect of changing two haptic rendering characteristics, the magnitude of friction and presence of haptic normal force shading, in combination with the role of stereoscopic displays and shadows, on the task of tracing 3D curves on systematically varied virtual surface geometry was studied. A higher simulated friction force increased drawing accuracy without slowing down the drawing speed by a statistically significant amount. The use of smooth, interpolated haptic normal force shading slightly improved speed but did not significantly affect accuracy. Stereo displays improved both drawing speed and accuracy, whereas the presence or absence of the shadow of the drawing tool had no statistically significant effect on either measure. In a follow-up user study, I studied the effect of varying stiffness and normal interpolation distance to improve the accuracy of surface path-following performance on faceted meshes rendered with haptic normal force shading. For single point haptic feedback simulated with a Sensable PHANToM arm, a formula for the just noticeable difference (JND) of stiffness was also derived. Higher stiffnesses reduced drawing errors up to a point, with an insignificant fall-off above an intermediate stiffness value of . 55N/mm. The normal interpolation distance did not affect errors. Better surface path-tracing accuracy was achieved by users who exerted lower forces, revealing shortcomings in the surface contact point calculation method used by GHOST. To address this limitation of haptic rendering systems that use polygonal boundary representations, I developed a new shape representation, multi-resolution distance-gradient volumes (MDGVs), and an associated interpolation method, a 3D extension of Coons patches with Hermite boundary curves. An MDGV stores, in octree vertices, the gradient of distances as well as the closest distance to the object being represented, to reduce alias artifacts near sharp features. The new interpolation method eliminates the positional discontinuities that occur with standard trilinearly interpolated distance fields at boundaries where cells that have different resolutions meet. The new haptic rendering system using MDGVs also reduces tangent discontinuities across cells, using considerably less time and space than uniformly sampled distance fields with tri-cubic interpolation. An algorithm that can compute the surface contact point efficiently using the first order approximation was developed to support haptically rendering thin objects. Friction forces and interactive low-pass filtering were implemented for a better haptic sketching interface on objects containing geometric features that prevent the user from interacting with them smoothly. The new haptic rendering system provides faster collision detection than haptic rendering systems using polygonal meshes of the same accuracy (two to three times faster in line-object collision detection). In the final user study, it has been demonstrated that users' performance in terms of path-following accuracy (near sharp edges) and speed was improved. In addition, it was found that having force feedback (rendered by GHOST or MDGVs) has advantages in accurate and precise path-following over not having force feedback.