Realistic haptic modeling & rendering of touch-enabled virtual environments

Virtual Reality (VR) applications strive to simulate real or imaginary scenes with which users can interact and perceive the effects of their actions in real time. Adding haptic information such as vibration, tactile array, force feedback simulation enhances the sense of presence in virtual environments. Realistic haptic modeling & rendering is the core component in feeling and manipulating virtual objects within the virtual environments. Haptics interfaces present new challenges in data processing analysis, physical modeling, interactive visualization and tangible simulations, especially in the situation where it is crucial for the operators to touch, grasp and manipulate rigid/soft objects in the virtual worlds. This thesis dissertation is mainly devoted to investigate the realistic haptics techniques in touch-enabled virtual environments. It has three major parts: the body-based haptic interaction model to simulate the realistic, physical tool-object interactions based on Hertz's contact theory and applications; the realization of interactive haptic manipulation of deformable objects with volume/surface representations, and further development of constrained haptic deformations based on the metaballs; the integration of multi-resolution rendering framework with level-of-detail impostor representations of graphics and haptics objects, to support the optimal rendering performance during the interactive navigation of touch-enabled virtual environments. The body-based haptic interaction model is proposed and developed for simulating the contacted forces between the haptic tools and interacting object, based on Hertz's theory establishing the intrinsic stress distribution related to real material properties. In comparison with the common force evaluation models, the proposed body-based haptic interaction model involves the intrinsic contacts with different tool/object materials acquired from the real world for the realistic haptics simulation. For adding the haptic sensations with touch-enabled soft objects, the thesis first studies multiple force-reflecting deformable objects in volume sculpting, then soft object deformation of Loop subdivision surfaces, and further the soft object freeform deformation through mass-spring Bezier volume lattice. The constrained haptic deformations based on the metaballs are experimented to effectively control the interactive force distribution within the influence range, making the deformable simulation of objects easy to control and manipulate. Lastly, the unified multi-resolution rendering framework of touch-enabled virtual environments is proposed and developed, with level-of-detail imposter representations of both graphics and haptics perceptions. The hierarchical graphics/haptics imposter descriptions of hybrid models (e.g. surfaces/volumes) within the virtual environment are constructed in advance, to maximize the optimal performance of the rendering processes during the interactive haptic-scene navigation and explorations. In comparison with other methods assuming that multi-contacts between tool and object are point or line based contacts, our body-based haptic interaction model involves the intrinsic contacts with different tool/object materials acquired from the real world for the realistic haptic simulation. Our studies in interactive haptic deformations is to marry the merits of traditional deformable modeling techniques in computer graphics with force-enabled deformations guided by real-world physics laws, simulating the realistic tangible sensation of interactive haptic manipulation with user-specified constraints in touch-enabled virtual environments. The multi-resolution rendering framework developed in our system unifies the graphics/haptics rendering processes based on the construction of hierarchical imposter representations of surface and volumetric models, and the optimal haptic-scene performance at run time is employed to meet both the visual and haptic perceptualqualities. The proposed work is extensible to support users perceptually experience the virtual objects with different materials through the tangible interfaces in the augmented virtual worlds. In general, haptic perception and manipulation can be further constructed uniformly in the multi-resolution rendering framework. The future work includes investigating multiple force evaluation methods and haptic contact models and in addition integrating them into the unified haptic-scene framework, for the rich and dexterous experiences in large, touch-enable virtual environments.