Radiosity for Virtual Reality Systems by Tralvex S L, Yeap A thesis submitted to School of Computer Studies in partial fulfilment of requirements for a degree of M. Sc. in Vision, Visualization and Virtual Environments University of Leeds Leeds, United Kingdom August 1997 © University of Leeds 1997 University of Leeds Abstract Radiosity for Virtual Reality Systems Supervisor : Professor Graham M. Birtwistle The synthesis of actual and computer generated photo-realistic images has been the aim of artists and graphic designers for many decades. Some of the most realistic images were generated using radiosity techniques. Unlike ray tracing, radiosity models the actual interaction between the light and its environment. In photo realistic Virtual Reality (VR) environments, the need for quick feedback based on user actions is crucial. It is generally recognised that traditional implementation of radiosity is computationally very expensive and therefore not feasible for use in VR systems where practical data sets are of huge complexity. To achieve photo-realism in images, we look into what radiosity can offer and the current state of art by doing a radiosity trend analysis. In addition, we also review several acceleration techniques which are suitable for applying radiosity in the synthesis of VR environments. Finally, we introduce two new methods and several hybrid techniques to the radiosity research community for using radiosity in VR applications. Acknowledgements This thesis would have been mission impossible if not for all those mentioned here. Many many thanks to: Ian Ashdown, an advisor as well as a friend whom I met on the Internet for sharing his knowledge in radiosity as well as his wide bibliographic collection on radiosity literature (more than 1100 papers). This has allowed me to do a radiosity trends analysis based on his bibliography as well as speeding up my search for specific paper. Prof. Donald P. Greenberg, Prof. Philip M. Hubbard, Dr. Al Z, Dr. Brian Smits, Dr. Eric Lafortune, Dr. Erik Robson, Dr. Luc Renambot, Dr. Neil Gatenby, Dr. Sumant Pattanaik, Ali Anghaie, Antonio Costa, Abraham Kee, Defee Pawel, Erik Robson, Gregory Ward, Ian Ashdown, Luc Renambot, Martin Thompson, Neil Gatenby, Rakesh Malik, Rob Love, Terrance Wong, Wim Dumon who took part in the survey correspondences on radiosity, sharing their practical experiences and knowledge. Graham Birtwistle for recommending Brian and Prezemek since day 1 of this thesis. Thanks for being a wonderful supervisor and for proof-reading all the drafts. I am always amazed by his creativity such as his suggestions on doing a trends analysis, the idea on thesis road maps, the compilation on "Selected Papers on Radiosity" book and many other brilliant recommendations. Wow! Tracy Goh, my beloved fiancee for devoting enormous amount of time and effort in proof-reading the drafts and also for her unlimited love and support throughout the M. Sc. programme, which kept me emotionally strong and going. Dennis Bell (MA in Education) and Azman Said (was an English teacher now doing MA in Mass Communication) for proof-reading my drafts. Dan Yeap for working on the SysEng logo (back in 1995) and correspondences on Computer Graphics - rendering aspects and the more complicated part of 3D Studio v4.0. Ken Brodlie and Terence Fernando for introducing me to the theoretical world of Scientific Visualisation and Advanced Computer Graphics, which otherwise I would be still stuck in the hacking world of CG! Ong Lee Haw and Lim Huiling for beta-testing the web materials in the CDROM using various web browers. Stuart Butterfield and Neil Sumpter for helping me out with the camcorder and the CDROM authoring. SCS Support for rendering their unlimited help and support in terms of the computing facilities. Brian Wyvill for giving me the initial boost by showing my where to find good sources of information for Computer Graphics - Radiosity materials, in particular works by Donald P. Greenberg. Przemek Prusinkiewicz for recommending useful books on radiosity since day 1. Neo Kwakwa (reading MSc in Combustion and Energy, LU) who shared with me, his knowledge in radiative heat transfer concepts and materials. Defence Science Organisation for expressing their interest in my thesis, which inspired me to do an even better thesis! Classic FM UK Radio Broadcasting station for supplying me unlimited doses of excellent classical music to boost my brain power and inspiration for this thesis and the M. Sc. programme! Mary Morris (place where I stayed) M flat shower room, where many knotty problems in the understanding of radiosity were solved. Very eerie but true. Contents 1 Introduction 1 1.1 Overview . 1 1.2 Goal of This Work . 1 1.3 Organisation of Thesis . 2 1.4 Research Methods . 3 1.5 Our Contributions . 3 2 Radiometry and Photometry 4 2.1 Introduction . 4 2.2 Mathematics Preliminary . 5 2.2.1 Solid Angles . 5 2.3 Radiometry . 6 2.3.1 Radiant Energy . 7 2.3.2 Radiant Flux (Radiant Power) . 7 2.3.3 Irradiance and Radiant Exitance . 8 2.3.4 Radiant Intensity . 8 2.3.5 Radiance . 9 2.4 Photometry . 10 2.4.1 Luminous energy . 11 2.4.2 Luminous Flux . 11 2.4.3 Illuminance and Luminous Exitance . 11 2.4.4 Luminous Intensity . 11 2.4.5 Luminance . 12 2.5 Summary . 12 3 Traditional Illumination and Shading Models 13 3.1 Introduction . 13 3.2 Illumination Models . 14 3.2.1 Ambient Reflection. 14 3.2.2 Diffuse Reflection . 14 3.2.3 Specular Reflection . 15 3.3 Shading Models . 15 3.3.1 Flat Shading . 15 3.3.2 Gouraud Shading . 16 3.3.3 Phong Shading . 16 3.3.4 Ray Tracing . 17 3.4 Summary . 17 4 Radiosity Principles 18 4.1 Introduction . 18 4.1.1 Lambertian Surfaces . 19 4.2 Radiosity Rendering Pipeline . 21 4.3 Meshing the Environment . 21 4.3.1 Uniform Mesh . 22 4.3.2 Higher Density Uniform Mesh . .. 23 4.3.3 Non-uniform Mesh . 23 4.4 The Radiosity Equation . 24 4.4.1 Concept of Form Factor . 24 4.4.1.1 Form Factors between Differential Areas . 25 4.4.1.2 Form Factors between Finite Area Patches . 26 4.4.1.3 Reciprocity Relationship between Form Factors . 27 4.4.1.4 Summation Relation . 27 4.4.1.5 Assumptions . 27 4.4.2 Form Factor Computation using Hemicube . 28 4.5 The Radiosity Equation Revisited . 29 4.6 Summary . 30 5 Radiosity Trend Analysis 31 5.1 Introduction . 31 5.2 Trend Analysis . 32 5.3 Literature Review . 33 5.3.1 Class R Literature Review . 33 5.3.2 Class S Literature Review . 34 5.3.3 Class H Literature Review . 35 5.3.4 Class V Literature Review . 36 5.4 Summary . 36 6 Accelerated Techniques for Radiosity 37 6.1 Introduction . 37 6.1.1 What is Virtual Reality? . 38 6.2 Extended Radiosity Pipeline . 38 6.3 Accelerated Techniques for Surface Meshing Stage . 39 6.3.1 Adaptive Meshing . 39 6.3.2 Radiosity Textures . 40 6.4 Accelerated Techniques for Form Factor Computation Stage . 42 6.4.1 Monte Carlo Methods for Radiosity . 43 6.5 Accelerated Techniques for Solving Radiosity Equation Stage . 45 6.5.1 Progressive Radiosity . 45 6.5.2 Parallel Progressive Radiosity . 47 6.6 Accelerated Techniques for Virtual Reality Engine Stage . 49 6.7 Summary . 49 7 Novel Approaches for VR Applications 50 7.1 Introduction . 50 7.2 First Novel Approach . 51 7.2.1 Background: Progressive Meshes . 52 7.2.2 Progressive Meshes Progressive Radiosity . 53 7.2.3 A Parallel Solution for PMPR . 56 7.2.4 Potential Hybrids . 58 7.3 Second Novel Approach . 60 7.3.1 Background: Point Distribution Model . 61 7.3.2 Background: Neural Networks. 62 7.3.3 Motion Prediction with PDM . 63 7.3.4 Potential Hybrids . 66 7.4 Summary . 66 8 The Road Ahead and Conclusion 66 8.1 Introduction . 66 8.2 The Road Ahead . 67 8.3 Contributions . 70 8.4 Future Work . 71 A Colour Figures 72 B Radiosity Survey Results 79 B.1 Introduction . 79 B.2 Results . 80 B.2.1 Is radiosity your preferred solution for generating realistic images? Why? If not, what are yours? . 80 B.2.2 What are the radiosity renderers in the market? . 82 B.2.3 What are the efficient ways to speed up computation of radiosity? . 82 B.2.4 What are the alternatives which produce better quality images than radiosity, or in general, for global illumination solutions? . 83 B.2.5 Where are the good places to look for radiosity resources? . 84 B.2.6 What is the future for radiosity in computer graphics? . 84 B.3 Actual Email Message Questionnaire/Survey . 86 C Radiosity Illustrations 87 C.1 Illustrations . 87 D Walk-throughs Screen Snapshots 90 D.1 Introduction . 90 D.1.1. Initial Stage Snapshots . 90 D.1.2 One-third Stage Snapshots . 91 D.1.3 Two-third Stage Snapshots . 91 D.1.4 Final Stage Snapshots . 92 E Contents of Book - “Selected Papers on Radiosity” 93 F Contents of CDROM 97 Bibliography List of Figures 1.1 Thesis Road Map. 2 2.1 Chapter 2 Road Map. 4 2.2 (a) A two dimensional circle with angle, q. (b) A three-dimensional sphere with solid angle, w. 5 2.3 A ray of light intersecting a surface . 6 2.4 (a) Irradiance. (b) Radiant exitance. 8 2.5 (a) Radiance (arriving). (b) Radiance (leaving). 9 2.6 Luminous efficiency function. 10 3.1 Chapter 3 Road Map. ..