Doctor of Philosophy

dissertationVirtual environments provide a consistent and relatively inexpensive method of training individuals. They often include haptic feedback in the form of forces applied to a manipulandum or thimble to provide a more immersive and educational experience. However, the limited haptic feedback provided in these systems tends to be restrictive and frustrating to use. Providing tactile feedback in addition to this kinesthetic feedback can enhance the user's ability to manipulate and interact with virtual objects while providing a greater level of immersion. This dissertation advances the state-of-the-art by providing a better understanding of tactile feedback and advancing combined tactilekinesthetic systems. The tactile feedback described within this dissertation is provided by a finger-mounted device called the contact location display (CLD). Rather than displaying the entire contact surface, the device displays (feeds back) information only about the center of contact between the user's finger and a virtual surface. In prior work, the CLD used specialized two-dimensional environments to provide smooth tactile feedback. Using polygonal environments would greatly enhance the device's usefulness. However, the surface discontinuities created by the facets on these models are rendered through the CLD, regardless of traditional force shading algorithms. To address this issue, a haptic shading algorithm was developed to provide smooth tactile and kinesthetic interaction with general polygonal models. Two experiments were used to evaluate the shading algorithm. iv To better understand the design requirements of tactile devices, three separate experiments were run to evaluate the perception thresholds for cue localization, backlash, and system delay. These experiments establish quantitative design criteria for tactile devices. These results can serve as the maximum (i.e., most demanding) device specifications for tactile-kinesthetic haptic systems where the user experiences tactile feedback as a function of his/her limb motions. Lastly, a revision of the CLD was constructed and evaluated. By taking the newly evaluated design criteria into account, the CLD device became smaller and lighter weight, while providing a full two degree-of-freedom workspace that covers the bottom hemisphere of the finger. Two simple manipulation experiments were used to evaluate the new CLD device

Procedural Planet Generation

Procedural planet generation is a way of creating interesting, computer-generated environments from a set of specified guidelines. When displaying these environments, only enough detail needs to be present so that the current view seems realistic. This can be accomplished by using simplified versions of the objects until more detail is required. This paper describes how to accomplish this level of detail switching using progressive meshes and describes a specific implementation of the simplification mechanism used to generate them

Sensory Communication

Contains table of contents for Section 2, an introduction and reports on fourteen research projects.National Institutes of Health Grant RO1 DC00117National Institutes of Health Grant RO1 DC02032National Institutes of Health/National Institute on Deafness and Other Communication Disorders Grant R01 DC00126National Institutes of Health Grant R01 DC00270National Institutes of Health Contract N01 DC52107U.S. Navy - Office of Naval Research/Naval Air Warfare Center Contract N61339-95-K-0014U.S. Navy - Office of Naval Research/Naval Air Warfare Center Contract N61339-96-K-0003U.S. Navy - Office of Naval Research Grant N00014-96-1-0379U.S. Air Force - Office of Scientific Research Grant F49620-95-1-0176U.S. Air Force - Office of Scientific Research Grant F49620-96-1-0202U.S. Navy - Office of Naval Research Subcontract 40167U.S. Navy - Office of Naval Research/Naval Air Warfare Center Contract N61339-96-K-0002National Institutes of Health Grant R01-NS33778U.S. Navy - Office of Naval Research Grant N00014-92-J-184

Isosurface extraction and haptic rendering of volumetric data.

Kwong-Wai, Chen.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 114-118).Abstracts in English and Chinese.Abstract --- p.iAcknowledgments --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Volumetric Data --- p.1Chapter 1.2 --- Volume Visualization --- p.4Chapter 1.3 --- Thesis Contributions --- p.5Chapter 1.4 --- Thesis Outline --- p.6Chapter I --- Multi-body Surface Extraction --- p.8Chapter 2 --- Isosurface Extraction --- p.9Chapter 2.1 --- Previous Works --- p.10Chapter 2.1.1 --- Marching Cubes --- p.10Chapter 2.1.2 --- Skeleton Climbing --- p.12Chapter 2.1.3 --- Adaptive Skeleton Climbing --- p.14Chapter 2.2 --- Motivation --- p.17Chapter 3 --- Multi-body Surface Extraction --- p.19Chapter 3.1 --- Multi-body Surface --- p.19Chapter 3.2 --- Building 0-skeleton --- p.21Chapter 3.3 --- Building 1-skeleton --- p.23Chapter 3.3.1 --- Non-binary Faces --- p.24Chapter 3.3.2 --- Non-binary Cubes --- p.30Chapter 3.4 --- General Scheme for Messy Cubes --- p.33Chapter 3.4.1 --- Graph Reduction --- p.34Chapter 3.4.2 --- Position of the Tetrapoints --- p.36Chapter 3.5 --- Triangular Mesh Generation --- p.37Chapter 3.5.1 --- Generating the Edge Loops --- p.38Chapter 3.5.2 --- Triangulating the Edge Loops --- p.41Chapter 3.5.3 --- Incorporating with Adaptive Skeleton Climbing --- p.43Chapter 3.6 --- Implementation and Results --- p.45Chapter II --- Haptic Rendering of Volumetric Data --- p.60Chapter 4 --- Introduction to Haptics --- p.61Chapter 4.1 --- Terminology --- p.62Chapter 4.2 --- Haptic Rendering Process --- p.63Chapter 4.2.1 --- The Overall Process --- p.64Chapter 4.2.2 --- Force Profile --- p.65Chapter 4.2.3 --- Decoupling Processes --- p.66Chapter 4.3 --- The PHANToM´ёØ Haptic Interface --- p.67Chapter 4.4 --- Research Goals --- p.69Chapter 5 --- Haptic Rendering of Geometric Models --- p.70Chapter 5.1 --- Penalty Based Methods --- p.71Chapter 5.1.1 --- Vector Fields for Solid Objects --- p.71Chapter 5.1.2 --- Drawbacks of Penalty Based Methods --- p.72Chapter 5.2 --- Constraint Based Methods --- p.73Chapter 5.2.1 --- Virtual Haptic Interface Point --- p.73Chapter 5.2.2 --- The Constraints --- p.74Chapter 5.2.3 --- Location Computation --- p.78Chapter 5.2.4 --- Force Shading --- p.79Chapter 5.2.5 --- Adding Surface Properties --- p.80Chapter 6 --- Haptic Rendering of Volumetric Data --- p.83Chapter 6.1 --- Volume Haptization --- p.84Chapter 6.2 --- Isosurface Haptic Rendering --- p.86Chapter 6.3 --- Intermediate Representation Approach --- p.89Chapter 6.3.1 --- Introduction --- p.89Chapter 6.3.2 --- Intermediate Virtual Plane --- p.90Chapter 6.3.3 --- Updating Virtual Plane --- p.92Chapter 6.3.4 --- Preventing Force Discontinuity Artifacts --- p.93Chapter 6.3.5 --- Experiments and Results --- p.94Chapter 7 --- Conclusions and Future Research Directions --- p.98Chapter 7.1 --- Conclusions --- p.98Chapter 7.2 --- Future Research Directions --- p.99Chapter A --- Two Proofs of Multi-body Surface Extraction Algorithm --- p.101Chapter A.1 --- Graph Terminology and Theorems --- p.101Chapter A.2 --- Occurrence of Tripoints in Negative-Positive Pairs --- p.103Chapter A.3 --- Validity of the General Scheme --- p.103Chapter B --- An Example of Multi-body Surface Extraction Algorithm --- p.105Chapter B.1 --- Step 1: Building 0-Skeleton --- p.105Chapter B.2 --- Step 2: Building 1-Skeleton --- p.106Chapter B.2.1 --- Step 2a: Building 1-Skeleton and Tripoints on Cube Faces --- p.106Chapter B.2.2 --- Step 2b: Adding Tetrapoints and Tri-edges inside Cube --- p.106Chapter B.3 --- Step 3: Constructing Edge Loops and Triangulating --- p.109Bibliography --- p.11

Interactive crayon rendering for animation

This thesis describes the design and implementation of an interactive, nonphotorealistic rendering system for three-dimensional computer animation. The system provides a two-dimensional interface for coloring successive frames of animation using a virtual crayon that emulates the appearance of hand-drawn wax crayons on textured paper. The crayon strokes automatically track and move with threedimensional objects in the animation to preserve temporal coherency of strokes from one frame to the next. The system is intended to be used as an interactive renderer in conjunction with third-party three-dimensional modeling and animation tools

Arbitrary topology meshes in geometric design and vector graphics

Meshes are a powerful means to represent objects and shapes both in 2D and 3D, but the techniques based on meshes can only be used in certain regular settings and restrict their usage. Meshes with an arbitrary topology have many interesting applications in geometric design and (vector) graphics, and can give designers more freedom in designing complex objects. In the first part of the thesis we look at how these meshes can be used in computer aided design to represent objects that consist of multiple regular meshes that are constructed together. Then we extend the B-spline surface technique from the regular setting to work on extraordinary regions in meshes so that multisided B-spline patches are created. In addition, we show how to render multisided objects efficiently, through using the GPU and tessellation. In the second part of the thesis we look at how the gradient mesh vector graphics primitives can be combined with procedural noise functions to create expressive but sparsely defined vector graphic images. We also look at how the gradient mesh can be extended to arbitrary topology variants. Here, we compare existing work with two new formulations of a polygonal gradient mesh. Finally we show how we can turn any image into a vector graphics image in an efficient manner. This vectorisation process automatically extracts important image features and constructs a mesh around it. This automatic pipeline is very efficient and even facilitates interactive image vectorisation

Design and development of a VR system for exploration of medical data using haptic rendering and high quality visualization

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Doctor of Philosophy

dissertationVirtual reality is becoming a common technology with applications in fields such as medical training, product development, and entertainment. Providing haptic (sense of touch) information along with visual and audio information can create an immersive vi

Visualization and analysis of diffusion tensor fields

technical reportThe power of medical imaging modalities to measure and characterize biological tissue is amplified by visualization and analysis methods that help researchers to see and understand the structures within their data. Diffusion tensor magnetic resonance imaging can measure microstructural properties of biological tissue, such as the coherent linear organization of white matter of the central nervous system, or the fibrous texture of muscle tissue. This dissertation describes new methods for visualizing and analyzing the salient structure of diffusion tensor datasets. Glyphs from superquadric surfaces and textures from reactiondiffusion systems facilitate inspection of data properties and trends. Fiber tractography based on vector-tensor multiplication allows major white matter pathways to be visualized. The generalization of direct volume rendering to tensor data allows large-scale structures to be shaded and rendered. Finally, a mathematical framework for analyzing the derivatives of tensor values, in terms of shape and orientation change, enables analytical shading in volume renderings, and a method of feature detection important for feature-preserving filtering of tensor fields. Together, the combination of methods enhances the ability of diffusion tensor imaging to provide insight into the local and global structure of biological tissue

Real-time hybrid cutting with dynamic fluid visualization for virtual surgery

It is widely accepted that a reform in medical teaching must be made to meet today's high volume training requirements. Virtual simulation offers a potential method of providing such trainings and some current medical training simulations integrate haptic and visual feedback to enhance procedure learning. The purpose of this project is to explore the capability of Virtual Reality (VR) technology to develop a training simulator for surgical cutting and bleeding in a general surgery