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Advanced Volume Rendering

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Advanced Volume Rendering ADVANCED VOLUME RENDERING DISSERTATION Presented in Partial Fulfillment of the Requirement for The Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Caixia Zhang, M.S. * * * * * The Ohio State University 2006 Dissertation Committee: Approved by Professor Roger Crawfis, Adviser Professor Raghu Machiraju Adviser Computer Science and Engineering Professor Han-Wei Shen Graduate Program ABSTRACT Although many advances have been achieved within the visualization community in the last decade, many challenging problems are still open in volume rendering: high- dimensional rendering, time-varying datasets, large datasets, complex flow fields, improvement of rendering accuracy, fidelity and interactivity, interdisciplinary research with other application communities, and so on. In this thesis, we study three challenging topics in advanced volume rendering: volumetric shadow and soft shadow algorithm in order to generate more realistic scenes; interval volumes and time-varying interval volumes for structured and unstructured grids; and implicit flow fields for three-dimensional flow visualization. A shadow is a region of relative darkness within an illuminated region caused by an object totally or partially occluding a light source. Shadows are essential to realistic and informative scenes. In volume rendering, the shadow calculation is difficult because the light intensity is attenuated as the light traverses the volume. We investigate a new shadow algorithm that properly determines the light attenuation and generates shadows for volumetric datasets, by using a 2D shadow buffer to keep track of the light attenuation through the volumetric participating media. Our shadow algorithm can generate accurate shadows with low storage requirements. The generation of soft shadows is a challenging ii topic in computer graphics which requires integrating the contributions of extended light sources on the illumination of objects. We have extended our shadow algorithm to deal with extended light sources and generate volumetric soft shadows with an analytic method and using a convolution technique. This shadow and soft shadow algorithm also has been applied to mixed scenes of volumetric and polygonal objects. Multiple light scattering is also modeled in our volumetric lighting model. Interval volume algorithm is a region-of-interest extraction algorithm for steady and time-varying three-dimensional structured and unstructured grids. A high-dimensional iso-surface algorithm is used to construct interval volumes. The algorithm is independent of the dimension and topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement for volume rendering of unstructured grids. We present several new rendering operations to provide effective visualizations of the 3D scalar field, and illustrate the use of interval volumes to highlight contour boundaries or material interfaces. This interval volume technique has been extended to four dimensions to extract time-varying interval volumes, using five-dimensional iso-contour construction. The time-varying interval volumes are rendered directly, from 4-simplices to image space, allowing us to visualize the integrated interval volumes over the time period and see how interval volumes change over time in a single view. Three-dimensional flow visualization is a challenging topic due to clutter, occlusion, and lack of depth perception cues in three dimensions. We propose an implicit flow field method to visualize 3D flow fields. An implicit flow field is first extracted using an advection operator on the flow, with a set of flow-related attributes stored. Two techniques are then employed to render the implicit flow field: a slice-based three- iii dimensional texture mapping approach and an interval volume approach. In the first technique, the implicit flow representation is loaded as a 3D texture and manipulated using a dynamic texture operation that allows the flow to be investigated interactively. In the second technique, a geometric flow volume is extracted from the implicit flow and rendered using the projected tetrahedron method implemented with the graphics hardware. With the second technique, we can achieve a complete system which can render streamlines, time-lines, stream surfaces, time surfaces and stream volumes together. iv Dedicated to my daughter, my husband and my parents v ACKNOWLEDGMENTS I would like to express my most sincere appreciation and gratitude to my adviser, Dr. Roger Crawfis, for his guidance, encouragement and solid support, which made this dissertation possible. It is his enthusiasm and guidance that bring me to this new field of visualization. His insights, research motivation and solid professional knowledge guide me through a lot of challenges. Without his guidance and assistance, this dissertation would not be possible. I would also like to thank Dr. Raghu Machiraju and Dr. Han-Wei Shen for giving me valuable suggestions during my research, reading my dissertation and acting as my defense committee. Another thank should be given to Dr. Rephael Wenger for his valuable guidance and sample code in the time-varying interval volume extraction. A special thank should be given to Daqing Xue, my colleague. We worked together, and came up with some ideas and good implementation from numerous discussions during my study and research in the graphics group. Also I want to thank him for his help in the implementation using the graphics hardware. I wish to thank Ming Jiang, Chaoli Wang, Guangfeng Ji, Liya Li, and all other students in the graphics group for their open discussions and valuable help. I spent a very happy life with them during my graduate study. vi VITA July10, 1973……………………………………Born – Taiyuan, Shanxi Province, China 1994…………………………………………… B.S. University of Science and Technology Beijing, China 1997…………………………………………….M.S. University of Science and Technology Beijing, China September 1998 – August 1999………………..University Fellowship, The Ohio State University September 1999 – March 2001…………………Graduate Research Associate, The Ohio State University 2001…………………………………………….M.S. Industrial and Systems Engineering The Ohio State University 2002…………………………………………….M.S. Computer and Information Science The Ohio State University June – September, 2005………………………..Summer Intern, Siemens Medical Solutions, Princeton, NJ September 2001 – present……………………...Graduate Research and Teaching Associate, The Ohio State University PUBLICATIONS Research Publication 1. Caixia Zhang, Praveen Bhaniramka, Daqing Xue, Roger Crawfis, Rephael Wenger, “Interval Volumes: Scalar Representations for Static and Time-Varying Data”, submitted for journal publication (2006). vii 2. Roger Crawfis, Leila De Floriani, Michael Lee, Caixia Zhang, “Modeling and Rendering Time-varying Scalar Fields”, submitted to Dagstuhl Scientific Visualization 2005 Proceedings. 3. Caixia Zhang, Daqing Xue, Roger Crawfis, Rephael Wenger, “Time-Varying Interval Volumes”, International Workshop on Volume Graphics 2005, pp.99-107, 2005. 4. Caixia Zhang, Roger Crawfis, “Light Propagation for Mixed Polygonal and Volumetric Data”, Computer Graphics International 2005, pp.249-256, 2005. 5. Daqing Xue, Caixia Zhang, Roger Crawfis, “iSBVR: Isosurface-aided Hardware Acceleration Techniques for 3D Slice-Based Volume Rendering”, International Workshop on Volume Graphics 2005, pp.207-215, 2005. 6. Praveen Bhaniramka, Caixia Zhang, Daqing Xue, Roger Crawfis, Rephael Wenger, “Volume Interval Segmentation and Rendering”, IEEE Volume Visualization 2004 Symposium, pp.55-62, 2004 (Best Paper). 7. Daqing Xue, Caixia Zhang, Roger Crawfis, “Rendering Implicit Flow Volumes”, IEEE Visualization 2004, pp.99-106, 2004. 8. Roger Crawfis, Daqing Xue, Caixia Zhang, “Volume Rendering Using Splatting, A Tutorial and Survey”, Visualization Handbook, eds. Charles Hansen, Christopher Johnson, Academic Press, 2004. 9. Ming Jiang, Naeem Shareef, Caixia Zhang, Roger Crawfis, Raghu Machiraju, Han-Wei Shen, “Visualization Fusion: Hurricane Isabel Dataset”, Technical Report OSU-CISRC-10/04- TR59, The Ohio State University, October 2004. 10. Caixia Zhang, Roger Crawfis, “Shadows and Soft Shadows with Participating Media Using Splatting”, IEEE Transactions on Visualization and Computer Graphics, vol. 9, no. 2, pp.139-149, 2003. 11. Caixia Zhang, Roger Crawfis, “Volumetric Shadows Using Splatting”, IEEE Visualization 2002, pp.85-92, 2002. FIELDS OF STUDY Major Field: Computer Science and Engineering Minor Field: Computer Networking Minor Field: Computer Architecture viii TABLE OF CONTENTS Page Abstract……………………………………………………………………………………ii Dedication…………………………………………………………………………….…...v Acknowledgments………………………………………………………………………..vi Vita………………………………………………………………………………………vii List of Tables…………………………………………………………………………….xii List of Figures…………………………………………………………………………...xiii Chapters: 1. Introduction………………………………………………………………………..1 1.1 General introduction…………………………………………………………..1 1.2 Introduction to volume rendering……………………………………………..2 1.3 Challenges and strategies……………………………………………………...8 1.3.1 Volumetric shadows and soft shadows……………………………...8 1.3.2 Interval volumes and time-varying interval volumes……………...10 1.3.3 Three-dimensional flow visualization……………………………...11 1.4 Contributions………………………………………………………………....13 1.5 Overview of dissertation……………………………………………………..17 2. Volumetric lighting models……………………………………………………...18 2.1 Introduction…………………………………………………………………..18 2.2 Previous work………………………………………………………………..19 2.2.1 Shadow algorithms…………………………………………………19
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