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UVA CS 445 - Level of Detail

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Level of DetailSlide 2Slide 3Slide 4IntroductionLevel of Detail: The Basic IdeaSlide 7Slide 8Level of Detail: MotivationLevel of Detail Research: GLODLevel of Detail: Traditional LOD In A NutshellSlide 12Level of Detail: The Big QuestionsSlide 14Slide 15Some BackgroundTraditional Approach: Discrete Level of DetailDiscrete LOD: AdvantagesSlide 19Discrete LOD: DisadvantagesDrastic Simplification: The Problem With Large ObjectsDrastic Simplification: The Problem With Small ObjectsDrastic SimplificationContinuous Level of DetailContinuous LOD: AdvantagesSlide 26Slide 27View-Dependent LOD: ExamplesSlide 29Slide 30Slide 31View-Dependent LOD: AdvantagesAn Aside: Hierarchical LODAn Aside: Hierarchical LODSummary: LOD FrameworksChoosing LODs: LOD Run-Time ManagementChoosing LODsSlide 38Choosing LODs Maintaining constant frame rateChoosing LODs: Maintaining constant frame rateChoosing LODs: Funkhouser & Sequin, SIGGRAPH 93The Big QuestionMeasuring FidelityMeasuring Visual FidelityPerceptual LODPerception 101: Contrast Sensitivity FunctionYour Personal CSFPerceptual Graphics: Where To Next?Level of DetailLevel of DetailDavid LuebkeUniversity of VirginiaLevel of DetailLevel of DetailDavid LuebkeUniversity of VirginiaLevel of DetailLevel of DetailDavid LuebkeUniversity of VirginiaLevel of DetailLevel of DetailDavid LuebkeUniversity of VirginiaIntroductionLevel of detail (LOD) is an important tool for maintaining interactivity–Focuses on the fidelity / performance tradeoff–Not the only tool! Complementary with:Parallel renderingOcclusion cullingImage-based rendering [etc]Level of Detail: The Basic IdeaThe problem: –Geometric datasets can be too complex to render at interactive ratesOne solution:–Simplify the polygonal geometry of small or distant objects–Known as Level of Detail or LODA.k.a. polygonal simplification, geometric simplification, mesh reduction, decimation, multiresolution modeling, …Level of DetailA recurring theme in computer graphics: trade fidelity for performance–Reduce level of detail of distant, small, or unimportant objects249,924 polys 62,480 polys 7,809 polys 975 polysLevel of DetailA recurring theme in computer graphics: trade fidelity for performance–Reduce level of detail of distant, small, or unimportant objectsLevel of Detail:MotivationBig models! –St. Matthew: 372 million polygons–David: 1 billion polygonsCourtesy Digital Michelangelo ProjectLevel of Detail Research:GLODGLOD: –High-level library for LOD in OpenGLGoal: make high-quality LOD easy to integrate in games and other graphics applicationsIncludes and interfaces with VDSlibCool software (interface design) issuesFree membership in the Church of Glöd–Show GLOD videoCourtesy Stanford 3D Scanning Repository69,451 polys 2,502 polys 251 polys 76 polysLevel of Detail:Traditional LOD In A NutshellCreate levels of detail (LODs) of objects:Distant objects use coarser LODs:Level of Detail:Traditional LOD In A NutshellLevel of Detail:The Big QuestionsHow to represent and generate simpler versions of a complex model?Courtesy Stanford 3D Scanning Repository69,451 polys 2,502 polys 251 polys 76 polysLevel of Detail:The Big QuestionsHow to evaluate the fidelity of the simplified models?Courtesy Stanford 3D Scanning Repository69,451 polys 2,502 polys 251 polys 76 polysLevel of Detail:The Big QuestionsWhen to use which LOD of an object?Courtesy Stanford 3D Scanning Repository69,451 polys 2,502 polys 251 polys 76 polysSome BackgroundHistory of LOD techniques–Early history: Clark (1976), flight simulators–Handmade LODs  automatic LODs–LOD run-time management: reactive  predictive (Funkhouser)LOD frameworks–Discrete (1976)–Continuous (1996)–View-dependent (1997)Traditional Approach: Discrete Level of DetailTraditional LOD in a nutshell:–Create LODs for each object separately in a preprocess–At run-time, pick each object’s LOD according to the object’s distance (or similar criterion)Since LODs are created offline at fixed resolutions, we call this discrete LODDiscrete LOD:AdvantagesSimplest programming model; decouples simplification and rendering–LOD creation need not address real-time rendering constraints–Run-time rendering need only pick LODsDiscrete LOD:AdvantagesFits modern graphics hardware well–Easy to compile each LOD into triangle strips, display lists, vertex arrays, …–These render much faster than unorganized triangles on today’s hardware (3-5 x)So why use anything but discrete LOD?Answer: sometimes discrete LOD not suited for drastic simplificationSome problem cases:–Terrain flyovers–Volumetric isosurfaces–Super-detailed range scans–Massive CAD modelsDiscrete LOD:DisadvantagesDrastic Simplification: The Problem With Large ObjectsCourtesy IBM and ACOGDrastic Simplification: The Problem With Small ObjectsCourtesy Electric BoatDrastic SimplificationFor drastic simplification:–Large objects must be subdivided–Small objects must be combinedDifficult or impossible with discrete LODSo what can we do?Continuous Level of DetailA departure from the traditional discrete approach:–Discrete LOD: create individual levels of detail in a preprocess–Continuous LOD: create data structure from which a desired level of detail can be extracted at run time.Continuous LOD:AdvantagesBetter granularity  better fidelity–LOD is specified exactly, not chosen from a few pre-created options–Thus objects use no more polygons than necessary, which frees up polygons for other objects –Net result: better resource utilization, leading to better overall fidelity/polygonContinuous LOD:AdvantagesBetter granularity  smoother transitions–Switching between traditional LODs can introduce visual “popping” effect–Continuous LOD can adjust detail gradually and incrementally, reducing visual popsCan even geomorph the fine-grained simplification operations over several frames to eliminate pops [Hoppe 96, 98]Continuous LOD:AdvantagesSupports progressive transmission–Progressive Meshes [Hoppe 97]–Progressive Forest Split Compression [Taubin 98]Leads to view-dependent LOD–Use current view parameters to select best representation for the current view–Single objects may thus span several levels of detailView-Dependent LOD: ExamplesShow nearby portions of object at higher resolution than distant portionsView from eyepointBirds-eye


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UVA CS 445 - Level of Detail

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