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Johns Hopkins CS 600 460 - Approaches to Polygonal Model Simplification

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Johns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenApproaches to Polygonal ModelSimplificationApproaches to Polygonal ModelApproaches to Polygonal ModelSimplificationSimplificationJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenGeometric ReplacementGeometric ReplacementGeometric ReplacementReplace complex objects with simplerReplace complex objects with simplerobjectsobjectsReduces transformation andReduces transformation andcommunication timecommunication timeRasterization time not changedRasterization time not changed••replacements should cover similar numberreplacements should cover similar numberof pixelsof pixelsJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenFord Bronco ModelFord Bronco ModelFord Bronco ModelTriangles:Triangles:41,85541,85527,97027,97020,92220,92212,93912,9398,3858,3854,7664,766courtesy of Division and Viewpointcourtesy of Division and ViewpointJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenAutomatic SimplificationAutomatic SimplificationAutomatic SimplificationPreprocessPreprocess••create multiresolution representationcreate multiresolution representationRun-timeRun-time••extract appropriate resolution model based onextract appropriate resolution model based onviewing parameters and rendering loadviewing parameters and rendering loadJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenImportant QuestionsImportant QuestionsImportant Questions1. What are the input restrictions?1. What are the input restrictions?2. How much is primitive count reduced?2. How much is primitive count reduced?3. How fast are primitives rendered?3. How fast are primitives rendered?4. How good can the results look?4. How good can the results look?5. How much space is used?5. How much space is used?6. How much pre-processing time?6. How much pre-processing time?Johns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenWhat I’ll Talk AboutWhat I’ll Talk AboutWhat I’ll Talk AboutPerforming SimplificationPerforming Simplification••Simplification OperationsSimplification Operations••Error MeasuresError MeasuresEmploying SimplificationEmploying Simplification••Static and Dynamic RepresentationsStatic and Dynamic Representations••Run-time ControlRun-time ControlJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenSimplification OperationsSimplification OperationsSimplification OperationsTypes of operationsTypes of operations••Vertex clusterVertex cluster••Vertex removeVertex remove••Edge collapseEdge collapse••Vertex pairVertex pairEach operation reduces model complexity byEach operation reduces model complexity bysmall amountsmall amountApply many operations in succession toApply many operations in succession toachieve large reductionsachieve large reductionsJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenVertex ClusterVertex ClusterVertex ClusterMerge vertices based on geometricMerge vertices based on geometricproximityproximityTriangles with repeated verticesTriangles with repeated verticesdegenerate to edge or pointdegenerate to edge or pointGeneral and robustGeneral and robustNot usually attractiveNot usually attractiveJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenVertex RemoveVertex RemoveVertex RemoveRemove vertex and adjacent facesRemove vertex and adjacent facesFill hole with new triangles (reduction of 2)Fill hole with new triangles (reduction of 2)••many possible triangulations (exponential)many possible triangulations (exponential)Requires Requires manifoldmanifold surface around vertex surface around vertexPreserves local topological structurePreserves local topological structure••typically more attractivetypically more attractiveJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenEdge CollapseEdge CollapseEdge CollapseMerge two edge vertices to oneMerge two edge vertices to one••choose position and attributes for vertexchoose position and attributes for vertexDelete degenerate trianglesDelete degenerate triangles••those containing both vertices (entire edge)those containing both vertices (entire edge)••2 triangles for manifold edge2 triangles for manifold edgeSmooth transitionsSmooth transitions••animate edge collapse(s) over timeanimate edge collapse(s) over timeJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenHalf-Edge CollapseHalf-Edge CollapseHalf-Edge CollapseCollapse to endpoint of edgeCollapse to endpoint of edge••Vertex subset property of vertex removeVertex subset property of vertex remove••Smooth transition property of edge collapseSmooth transition property of edge collapseJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenVertex Remove vs. Edge CollapseVertex Remove Vertex Remove vsvs. Edge Collapse. Edge CollapseVertex RemoveVertex Remove••Affects neighborhoodAffects neighborhoodaround 1 vertexaround 1 vertex••Does not introduce newDoes not introduce newverticesvertices••Many possible Many possible tesselationstesselations••Smooth transitionsSmooth transitionsdifficultdifficultVertexRemovesVertexRemovesEdgeCollapsesEdgeCollapsesHalf EdgeCollapsesHalf EdgeCollapsesEdge CollapseEdge Collapse••Affects neighborhoodAffects neighborhoodaround 2 verticesaround 2 vertices••Freely positions one newFreely positions one newvertexvertex••Single possible Single possible tesselationtesselation••Smooth transitionsSmooth transitionsnaturalnaturalJohns Hopkins Department of Computer ScienceCourse 600.460: Virtual Worlds, Spring 2000, Professor: Jonathan CohenVertex PairVertex PairVertex PairMerge any two verticesMerge any two vertices••based on geometry, topology, etc.based on geometry, topology, etc.More flexibility than edge collapseMore flexibility than edge collapseMore local control than vertex clusterMore


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