1. Quadric-Based Polygonal Surface Simplification Michael Garland Carnegie Mellon University December 1998 Michael Garland Carnegie Mellon University December 1998

2. Overview Polygonal models are often too complex Can be highly over-sampled (e.g., scanned data)Can be highly over-sampled (e.g., scanned data) Manage complexity given limited resourcesManage complexity given limited resources –rendering speed, network bandwidth, disk space,... Automatically build surface approximations Maintain geometric fidelity to originalMaintain geometric fidelity to original Produce approximations rapidlyProduce approximations rapidly Simplify topology as well as geometrySimplify topology as well as geometry Polygonal models are often too complex Can be highly over-sampled (e.g., scanned data)Can be highly over-sampled (e.g., scanned data) Manage complexity given limited resourcesManage complexity given limited resources –rendering speed, network bandwidth, disk space,... Automatically build surface approximations Maintain geometric fidelity to originalMaintain geometric fidelity to original Produce approximations rapidlyProduce approximations rapidly Simplify topology as well as geometrySimplify topology as well as geometry

3. Polygonal Surface Models Set of vertices Position in spacePosition in space Attributes (e.g., color)Attributes (e.g., color) Set of triangles All polygons are triangulatedAll polygons are triangulated Primary focus on rendering Appearance is paramountAppearance is paramount

4. Assumptions About Input Model Mesh connectivity is complete Corners which coincide in space share verticesCorners which coincide in space share vertices Surface need not have manifold topology Edges can border any number of facesEdges can border any number of faces Vertices shared by arbitrary collection of facesVertices shared by arbitrary collection of faces Consistent normal orientation not requiredConsistent normal orientation not required Application domain does not rely on topology vs. medical imaging — hole in the lung mattersvs. medical imaging — hole in the lung matters Mesh connectivity is complete Corners which coincide in space share verticesCorners which coincide in space share vertices Surface need not have manifold topology Edges can border any number of facesEdges can border any number of faces Vertices shared by arbitrary collection of facesVertices shared by arbitrary collection of faces Consistent normal orientation not requiredConsistent normal orientation not required Application domain does not rely on topology vs. medical imaging — hole in the lung mattersvs. medical imaging — hole in the lung matters

5. Motivation: Highly Over-sampled Models 424,376 faces 60,000 faces

6. Motivation: Adaptive Models for Rendering Single model not always suitable Too large for hardware capacityToo large for hardware capacity Excessively detailed for screen sizeExcessively detailed for screen size Use multiresolution models Encode many levels of detail (LOD)Encode many levels of detail (LOD) Adaptively select LOD at run timeAdaptively select LOD at run time Progressive network transmissionProgressive network transmission

7. Surface Simplification: Create suitable approximations

8. Desirable Qualities for Good Approximations Geometric fidelity — a proxy for appearance Shape is “similar” to the originalShape is “similar” to the original All points in close proximity to original surfaceAll points in close proximity to original surface Economical meshes Mesh density & aspect ratios adapt to curvatureMesh density & aspect ratios adapt to curvature Topological consistency Do not introduce self-intersectionsDo not introduce self-intersections But in practice, the input is often inconsistentBut in practice, the input is often inconsistent Geometric fidelity — a proxy for appearance Shape is “similar” to the originalShape is “similar” to the original All points in close proximity to original surfaceAll points in close proximity to original surface Economical meshes Mesh density & aspect ratios adapt to curvatureMesh density & aspect ratios adapt to curvature Topological consistency Do not introduce self-intersectionsDo not introduce self-intersections But in practice, the input is often inconsistentBut in practice, the input is often inconsistent

9. Features of My Surface Simplification Algorithm An effective algorithm for practical use Simple to implementSimple to implement Fast simplification (10,000 faces in 1 second)Fast simplification (10,000 faces in 1 second) High quality approximationsHigh quality approximations Implicitly simplifies topology All decisions are based on geometric criteriaAll decisions are based on geometric criteria Can manage surface properties Color, texture, etc.Color, texture, etc. An effective algorithm for practical use Simple to implementSimple to implement Fast simplification (10,000 faces in 1 second)Fast simplification (10,000 faces in 1 second) High quality approximationsHigh quality approximations Implicitly simplifies topology All decisions are based on geometric criteriaAll decisions are based on geometric criteria Can manage surface properties Color, texture, etc.Color, texture, etc.

10. contract v1v1v1v1 v2v2v2v2 v’ Fundamental Operation: Edge Contraction Contract vertex pair (v 1,v 2 )  v’ Move v 1 and v 2 to position v’Move v 1 and v 2 to position v’ Replace all occurrences of v 2 with v 1Replace all occurrences of v 2 with v 1 Remove v 2 and degenerate trianglesRemove v 2 and degenerate triangles Contract vertex pair (v 1,v 2 )  v’ Move v 1 and v 2 to position v’Move v 1 and v 2 to position v’ Replace all occurrences of v 2 with v 1Replace all occurrences of v 2 with v 1 Remove v 2 and degenerate trianglesRemove v 2 and degenerate triangles

11. Properties of Edge Contraction Local, fine-grained modification Low computational costLow computational cost Removes 2 faces + 1 vertex (on a closed manifold)Removes 2 faces + 1 vertex (on a closed manifold) Continuous transition Can linearly interpolate contraction through timeCan linearly interpolate contraction through time Allows smooth geomorphing between surfacesAllows smooth geomorphing between surfaces Its inverse, vertex split, has same properties Handy for progressive mesh transmission [Hoppe 96]Handy for progressive mesh transmission [Hoppe 96] Local, fine-grained modification Low computational costLow computational cost Removes 2 faces + 1 vertex (on a closed manifold)Removes 2 faces + 1 vertex (on a closed manifold) Continuous transition Can linearly interpolate contraction through timeCan linearly interpolate contraction through time Allows smooth geomorphing between surfacesAllows smooth geomorphing between surfaces Its inverse, vertex split, has same properties Handy for progressive mesh transmission [Hoppe 96]Handy for progressive mesh transmission [Hoppe 96]

12. Overview of Algorithm Preprocessing phase: model cleanup Enforce vertex sharingEnforce vertex sharing Triangulate & remove degenerate facesTriangulate & remove degenerate faces Iteratively contract vertex pairs (i.e., edges) Simple greedy techniqueSimple greedy technique Rank edges by “cost” of contractionRank edges by “cost” of contraction Maintain proposed contractions in a heapMaintain proposed contractions in a heap At each iteration, contract minimum cost edgeAt each iteration, contract minimum cost edge Preprocessing phase: model cleanup Enforce vertex sharingEnforce vertex sharing Triangulate & remove degenerate facesTriangulate & remove degenerate faces Iteratively contract vertex pairs (i.e., edges) Simple greedy techniqueSimple greedy technique Rank edges by “cost” of contractionRank edges by “cost” of contraction Maintain proposed contractions in a heapMaintain proposed contractions in a heap At each iteration, contract minimum cost edgeAt each iteration, contract minimum cost edge

13. Measuring Cost of Contractions Cost should reflect geometric error introduced Error between current & original (vs. last iteration)Error between current & original (vs. last iteration) Also want this to be fairly cheap to computeAlso want this to be fairly cheap to compute Various contraction-based algorithms differ here [Guéziec 95; Hoppe 96; Lindstrom-Turk 98; Ronfard-Rossignac 96]Various contraction-based algorithms differ here [Guéziec 95; Hoppe 96; Lindstrom-Turk 98; Ronfard-Rossignac 96] Must address two interrelated problems What is the best contraction to perform?What is the best contraction to perform? What is the best position v’ for remaining vertex?What is the best position v’ for remaining vertex? Cost should reflect geometric error introduced Error between current & original (vs. last iteration)Error between current & original (vs. last iteration) Also want this to be fairly cheap to computeAlso want this to be fairly cheap to compute Various contraction-based algorithms differ here [Guéziec 95; Hoppe 96; Lindstrom-Turk 98; Ronfard-Rossignac 96]Various contraction-based algorithms differ here [Guéziec 95; Hoppe 96; Lindstrom-Turk 98; Ronfard-Rossignac 96] Must address two interrelated problems What is the best contraction to perform?What is the best contraction to perform? What is the best position v’ for remaining vertex?What is the best position v’ for remaining vertex?

14. How I Measure Error Each vertex has a (conceptual) set of planes Error  sum of squared distances to planes in setError  sum of squared distances to planes in set Initialize with planes of incident faces Consequently, all initial errors are 0Consequently, all initial errors are 0 When contracting pair, use union of plane sets planes(v’) = planes(v 1 )  planes(v 2 )planes(v’) = planes(v 1 )  planes(v 2 ) Each vertex has a (conceptual) set of planes Error  sum of squared distances to planes in setError  sum of squared distances to planes in set Initialize with planes of incident faces Consequently, all initial errors are 0Consequently, all initial errors are 0 When contracting pair, use union of plane sets planes(v’) = planes(v 1 )  planes(v 2 )planes(v’) = planes(v 1 )  planes(v 2 )

15. A Simple Example: Contraction & “Planes” in 2D Lines defined by neighboring segments Determine position of new vertexDetermine position of new vertex Accumulate lines for ever larger areasAccumulate lines for ever larger areas Lines defined by neighboring segments Determine position of new vertexDetermine position of new vertex Accumulate lines for ever larger areasAccumulate lines for ever larger areas Original After 1 Step v1v1v1v1 v2v2v2v2v’

16. How I Measure Error Why base error on planes? Faster, but less accurate, than distance-to-faceFaster, but less accurate, than distance-to-face Simple linear system for optimal positionSimple linear system for optimal position Efficient implicit representation; no sets requiredEfficient implicit representation; no sets required Drawback: unlike surface, planes are infiniteDrawback: unlike surface, planes are infinite Related error metrics Ronfard & Rossignac — max vs. sumRonfard & Rossignac — max vs. sum Lindstrom & Turk — similar form; volume-basedLindstrom & Turk — similar form; volume-based Why base error on planes? Faster, but less accurate, than distance-to-faceFaster, but less accurate, than distance-to-face Simple linear system for optimal positionSimple linear system for optimal position Efficient implicit representation; no sets requiredEfficient implicit representation; no sets required Drawback: unlike surface, planes are infiniteDrawback: unlike surface, planes are infinite Related error metrics Ronfard & Rossignac — max vs. sumRonfard & Rossignac — max vs. sum Lindstrom & Turk — similar form; volume-basedLindstrom & Turk — similar form; volume-based

17. The Quadric Error Metric Given a plane, we can define a quadric Q measuring squared distance to the plane as

18. The Quadric Error Metric Sum of quadrics represents set of planes Each vertex has an associated quadric Error(v i ) = Q i (v i )Error(v i ) = Q i (v i ) Sum quadrics when contracting (v i, v j )  v’Sum quadrics when contracting (v i, v j )  v’ Cost of contraction is Q(v’)Cost of contraction is Q(v’) Sum of quadrics represents set of planes Each vertex has an associated quadric Error(v i ) = Q i (v i )Error(v i ) = Q i (v i ) Sum quadrics when contracting (v i, v j )  v’Sum quadrics when contracting (v i, v j )  v’ Cost of contraction is Q(v’)Cost of contraction is Q(v’)

19. The Quadric Error Metric Sum of endpoint quadrics determines v’ Fixed placement: select v 1 or v 2Fixed placement: select v 1 or v 2 Optimal placement: choose v’ minimizing Q(v’)Optimal placement: choose v’ minimizing Q(v’) Fixed placement is faster but lower qualityFixed placement is faster but lower quality But it also gives smaller progressive meshesBut it also gives smaller progressive meshes Fallback to fixed placement if A is non-invertibleFallback to fixed placement if A is non-invertible Sum of endpoint quadrics determines v’ Fixed placement: select v 1 or v 2Fixed placement: select v 1 or v 2 Optimal placement: choose v’ minimizing Q(v’)Optimal placement: choose v’ minimizing Q(v’) Fixed placement is faster but lower qualityFixed placement is faster but lower quality But it also gives smaller progressive meshesBut it also gives smaller progressive meshes Fallback to fixed placement if A is non-invertibleFallback to fixed placement if A is non-invertible

20. Sample Model: Scanned Bunny 69,451 faces 1000 faces 100 faces Total simplification time: 7 seconds 200 MHz PentiumPro; excludes input–output time200 MHz PentiumPro; excludes input–output time Shape preserved at 1000 faces; gross structure at 100 Total simplification time: 7 seconds 200 MHz PentiumPro; excludes input–output time200 MHz PentiumPro; excludes input–output time Shape preserved at 1000 faces; gross structure at 100

21. Additional Algorithm Details Open boundaries may be eaten away For each edge with a single incident faceFor each edge with a single incident face –Find constraint plane through edge perpendicular to face –Assign large weight & add into endpoints Contraction may fold mesh over onto itself Check normals before & after; reject if any flipCheck normals before & after; reject if any flip Error metric dependent on initial mesh Weight quadrics by triangle areaWeight quadrics by triangle area Open boundaries may be eaten away For each edge with a single incident faceFor each edge with a single incident face –Find constraint plane through edge perpendicular to face –Assign large weight & add into endpoints Contraction may fold mesh over onto itself Check normals before & after; reject if any flipCheck normals before & after; reject if any flip Error metric dependent on initial mesh Weight quadrics by triangle areaWeight quadrics by triangle area

22. Visualizing Quadrics in 3-D Quadric isosurfaces Are ellipsoids (maybe degenerate)Are ellipsoids (maybe degenerate) Centered around verticesCentered around vertices Characterize shapeCharacterize shape Stretch in least- curved directionsStretch in least- curved directions

23. Quadrics and Surface Curvature For quadrics on differentiable manifold Limit of infinitely subdivided polygonal surfaceLimit of infinitely subdivided polygonal surface Integrate quadrics in a small neighborhoodIntegrate quadrics in a small neighborhood Can prove that in the limit Eigenvectors of A are principal directionsEigenvectors of A are principal directions Eigenvalues of A  squared principal curvaturesEigenvalues of A  squared principal curvatures Algorithm which minimizes quadric error will produce optimal aspect ratios [Nadler 86, D’Azevedo 89]Algorithm which minimizes quadric error will produce optimal aspect ratios [Nadler 86, D’Azevedo 89] For quadrics on differentiable manifold Limit of infinitely subdivided polygonal surfaceLimit of infinitely subdivided polygonal surface Integrate quadrics in a small neighborhoodIntegrate quadrics in a small neighborhood Can prove that in the limit Eigenvectors of A are principal directionsEigenvectors of A are principal directions Eigenvalues of A  squared principal curvaturesEigenvalues of A  squared principal curvatures Algorithm which minimizes quadric error will produce optimal aspect ratios [Nadler 86, D’Azevedo 89]Algorithm which minimizes quadric error will produce optimal aspect ratios [Nadler 86, D’Azevedo 89]

24. Sample Model: Dental Mold 424,376 faces 60,000 faces 50 sec

25. Sample Model: Dental Mold 424,376 faces 8000 faces 55 sec

26. Sample Model: Dental Mold 424,376 faces 1000 faces 56 sec

27. Sample Model: Turbine Blade 1,765,388 faces 420,000 faces 217 sec

28. Sample Model: Turbine Blade 1,765,388 faces 80,000 faces 300 sec

29. Sample Model: Turbine Blade 1,765,388 faces 310 sec 8000 faces

30. Good Geometric Results, Need to Consider Attributes Fundamental algorithm works well Simple to implement & simplification is fastSimple to implement & simplification is fast High-quality approximationsHigh-quality approximations Quadrics record useful information about shapeQuadrics record useful information about shape But many models have additional properties Color, texture, normals, etc.Color, texture, normals, etc. Need to simplify these as wellNeed to simplify these as well Fundamental algorithm works well Simple to implement & simplification is fastSimple to implement & simplification is fast High-quality approximationsHigh-quality approximations Quadrics record useful information about shapeQuadrics record useful information about shape But many models have additional properties Color, texture, normals, etc.Color, texture, normals, etc. Need to simplify these as wellNeed to simplify these as well

31. Gouraud Shaded Surface: Single RGB Value Per Vertex Surface geometry Radiosity solution

32. Gouraud Shaded Surface: Single RGB Value Per Vertex Mesh for solution Radiosity solution

33. Surface Properties as Vertex Attributes Each vertex has a set of properties Each property has one unique value per vertexEach property has one unique value per vertex Attributes are linearly interpolated over facesAttributes are linearly interpolated over faces Primary example: one RGB color per vertexPrimary example: one RGB color per vertex Can’t treat geometry & color separately Position and color are correlatedPosition and color are correlated Optimal position may lie off the surfaceOptimal position may lie off the surface Must synthesize new color for this positionMust synthesize new color for this position Each vertex has a set of properties Each property has one unique value per vertexEach property has one unique value per vertex Attributes are linearly interpolated over facesAttributes are linearly interpolated over faces Primary example: one RGB color per vertexPrimary example: one RGB color per vertex Can’t treat geometry & color separately Position and color are correlatedPosition and color are correlated Optimal position may lie off the surfaceOptimal position may lie off the surface Must synthesize new color for this positionMust synthesize new color for this position

34. Vertex Attributes Become Added Dimensions Treat each vertex as a 6-vector [x y z r g b] Assume this 6-D space is EuclideanAssume this 6-D space is Euclidean –Of course, color space is only roughly Euclidean Scale xyz space to unit cube for consistencyScale xyz space to unit cube for consistency Triangle determines a 2-plane in 6-D space Can measure squared distance to this planeCan measure squared distance to this plane Distance along all perpendicular directionsDistance along all perpendicular directions –Generalized Pythagorean Theorem Treat each vertex as a 6-vector [x y z r g b] Assume this 6-D space is EuclideanAssume this 6-D space is Euclidean –Of course, color space is only roughly Euclidean Scale xyz space to unit cube for consistencyScale xyz space to unit cube for consistency Triangle determines a 2-plane in 6-D space Can measure squared distance to this planeCan measure squared distance to this plane Distance along all perpendicular directionsDistance along all perpendicular directions –Generalized Pythagorean Theorem

35. Generalized Quadric Metric Squared distance to 2-plane has same form: A: 6x6 matrix v,b: 6-vectors c: scalar (for RGB)A: 6x6 matrix v,b: 6-vectors c: scalar (for RGB) Underlying algorithm remains the sameUnderlying algorithm remains the same May want to selectively weight channels Relative importance of space & colorRelative importance of space & color Relative importance of red & greenRelative importance of red & green Squared distance to 2-plane has same form: A: 6x6 matrix v,b: 6-vectors c: scalar (for RGB)A: 6x6 matrix v,b: 6-vectors c: scalar (for RGB) Underlying algorithm remains the sameUnderlying algorithm remains the same May want to selectively weight channels Relative importance of space & colorRelative importance of space & color Relative importance of red & greenRelative importance of red & green

36. Generalized Quadric Metric Common property types VertexDimension VertexDimension Color[x y z r g b]6x6 quadricsColor[x y z r g b]6x6 quadrics Texture[x y z s t]5x5 quadricsTexture[x y z s t]5x5 quadrics Normal[x y z u v w]6x6 quadricsNormal[x y z u v w]6x6 quadrics Color+Normal[x y z r g b u v w]9x9 quadricsColor+Normal[x y z r g b u v w]9x9 quadrics Common property types VertexDimension VertexDimension Color[x y z r g b]6x6 quadricsColor[x y z r g b]6x6 quadrics Texture[x y z s t]5x5 quadricsTexture[x y z s t]5x5 quadrics Normal[x y z u v w]6x6 quadricsNormal[x y z u v w]6x6 quadrics Color+Normal[x y z r g b u v w]9x9 quadricsColor+Normal[x y z r g b u v w]9x9 quadrics

37. Simplifying the Dragon Model (xyzrgb quadrics) 50,761 faces 10,000 faces 20 sec.

38. Simplifying the Dragon Model (xyzrgb quadrics) 50,761 faces 1,500 faces 23 sec.

39. Simplifying the Dragon Model (xyzrgb quadrics) 50,761 faces 1,500 faces 23 sec.

40. A Sample Textured Surface

41. Simplifying Geometry Only: Same Texture Coordinates

42. Simplifying with xyzst Quadrics; New Texture Coordinates

43. Comparison to Related Work Vertex clustering [Rossignac–Borrel 93; Low–Tan 96] Partition space; merge vertices within cellsPartition space; merge vertices within cells More general: doesn’t require connectivityMore general: doesn’t require connectivity Very fast, but poor qualityVery fast, but poor quality Mesh optimization [Hoppe et al 93] Energy minimization approachEnergy minimization approach Very slow; highest quality resultsVery slow; highest quality results Vertex clustering [Rossignac–Borrel 93; Low–Tan 96] Partition space; merge vertices within cellsPartition space; merge vertices within cells More general: doesn’t require connectivityMore general: doesn’t require connectivity Very fast, but poor qualityVery fast, but poor quality Mesh optimization [Hoppe et al 93] Energy minimization approachEnergy minimization approach Very slow; highest quality resultsVery slow; highest quality results

44. Comparison to Related Work Vertex decimation [Schroeder et al 92, Schroeder 97] Error based on distance to plane of neighborhoodError based on distance to plane of neighborhood Appears somewhat slower, lower qualityAppears somewhat slower, lower quality Requires less memoryRequires less memory Vertex decimation [Soucy–Laurendeau 96, Klein et al 96] More extensive distance-to-surface measurementsMore extensive distance-to-surface measurements Good quality; rather slowGood quality; rather slow Vertex decimation [Schroeder et al 92, Schroeder 97] Error based on distance to plane of neighborhoodError based on distance to plane of neighborhood Appears somewhat slower, lower qualityAppears somewhat slower, lower quality Requires less memoryRequires less memory Vertex decimation [Soucy–Laurendeau 96, Klein et al 96] More extensive distance-to-surface measurementsMore extensive distance-to-surface measurements Good quality; rather slowGood quality; rather slow

45. Comparison to Related Work Iterative edge contraction Progressive mesh construction [Hoppe 96]Progressive mesh construction [Hoppe 96] –Very high quality; very slow Memory-less simplification [Lindstrom–Turk 98]Memory-less simplification [Lindstrom–Turk 98] –Similar quality; slower; uses less memory Full-range approximation [Ronfard–Rossignac 96]Full-range approximation [Ronfard–Rossignac 96] –Somewhat lower quality; slower; more memory Iterative edge contraction Progressive mesh construction [Hoppe 96]Progressive mesh construction [Hoppe 96] –Very high quality; very slow Memory-less simplification [Lindstrom–Turk 98]Memory-less simplification [Lindstrom–Turk 98] –Similar quality; slower; uses less memory Full-range approximation [Ronfard–Rossignac 96]Full-range approximation [Ronfard–Rossignac 96] –Somewhat lower quality; slower; more memory

46. Alternative Application: Partition Surface Geometry Partition into disjoint sets of faces Disjoint sets of connected facesDisjoint sets of connected faces Aggregate, rather than approximate, geometryAggregate, rather than approximate, geometry “Dual” simplification builds face regions Dual quadrics:Dual quadrics: Edge contraction in dual graphEdge contraction in dual graph –Each node is a face cluster; contraction merges clusters –Produces binary tree of hierarchical regions Partition into disjoint sets of faces Disjoint sets of connected facesDisjoint sets of connected faces Aggregate, rather than approximate, geometryAggregate, rather than approximate, geometry “Dual” simplification builds face regions Dual quadrics:Dual quadrics: Edge contraction in dual graphEdge contraction in dual graph –Each node is a face cluster; contraction merges clusters –Produces binary tree of hierarchical regions

47. Simplifying Dual Graph Partitions the Surface11,036 60001000 200

48. Summary: Primary Contributions Quadric error metric Efficient characterization of local surface shapeEfficient characterization of local surface shape Proven connection to surface curvatureProven connection to surface curvature Hierarchical face clustering Application of “dual” simplification algorithmApplication of “dual” simplification algorithm Partition, rather than approximate, geometryPartition, rather than approximate, geometry Quadric-based simplification algorithm... Quadric error metric Efficient characterization of local surface shapeEfficient characterization of local surface shape Proven connection to surface curvatureProven connection to surface curvature Hierarchical face clustering Application of “dual” simplification algorithmApplication of “dual” simplification algorithm Partition, rather than approximate, geometryPartition, rather than approximate, geometry Quadric-based simplification algorithm...

49. Summary: Quadric-Based Simplification Rapidly generate high quality approximations Good compromise between highest quality and fastest simplificationGood compromise between highest quality and fastest simplification Can simplify non-manifold surfacesCan simplify non-manifold surfaces Manages material properties as well as geometryManages material properties as well as geometry Doesn’t have guaranteed error boundsDoesn’t have guaranteed error bounds Currently in real-world use Scanned data, isosurfaces, CAD, VR, …Scanned data, isosurfaces, CAD, VR, … Rapidly generate high quality approximations Good compromise between highest quality and fastest simplificationGood compromise between highest quality and fastest simplification Can simplify non-manifold surfacesCan simplify non-manifold surfaces Manages material properties as well as geometryManages material properties as well as geometry Doesn’t have guaranteed error boundsDoesn’t have guaranteed error bounds Currently in real-world use Scanned data, isosurfaces, CAD, VR, …Scanned data, isosurfaces, CAD, VR, …

50. Future Directions Exploiting speed of simplification Interactive simplificationInteractive simplification Online generation of progressive meshesOnline generation of progressive meshes Exploiting resulting hierarchical structure Adaptive surface modelsAdaptive surface models –View-dependent refinement, multiresolution surface editing Hierarchical computationsHierarchical computations –Shape analysis, radiosity, collision detection Exploiting speed of simplification Interactive simplificationInteractive simplification Online generation of progressive meshesOnline generation of progressive meshes Exploiting resulting hierarchical structure Adaptive surface modelsAdaptive surface models –View-dependent refinement, multiresolution surface editing Hierarchical computationsHierarchical computations –Shape analysis, radiosity, collision detection

51. Future Directions Improving simplification De-coupling analysis & synthesis phasesDe-coupling analysis & synthesis phases More effective topological simplificationMore effective topological simplification Accommodate topological preservationAccommodate topological preservation Analysis of generalized quadric error metricAnalysis of generalized quadric error metric Application to tetrahedralized volumes A different kind of generalized quadricA different kind of generalized quadric Non-greedy quadric-based simplification Improving simplification De-coupling analysis & synthesis phasesDe-coupling analysis & synthesis phases More effective topological simplificationMore effective topological simplification Accommodate topological preservationAccommodate topological preservation Analysis of generalized quadric error metricAnalysis of generalized quadric error metric Application to tetrahedralized volumes A different kind of generalized quadricA different kind of generalized quadric Non-greedy quadric-based simplification

52. Acknowledgements Funded in part by NSF; Schlumberger FoundationNSF; Schlumberger Foundation Models used in presentation Stanford graphics lab — bunnyStanford graphics lab — bunny Iris Development — dental moldIris Development — dental mold Viewpoint DataLabs — dragonViewpoint DataLabs — dragon GE/KitWare — turbine blade, heat exchangerGE/KitWare — turbine blade, heat exchanger Andrew Willmott — radiosity solutionAndrew Willmott — radiosity solution Funded in part by NSF; Schlumberger FoundationNSF; Schlumberger Foundation Models used in presentation Stanford graphics lab — bunnyStanford graphics lab — bunny Iris Development — dental moldIris Development — dental mold Viewpoint DataLabs — dragonViewpoint DataLabs — dragon GE/KitWare — turbine blade, heat exchangerGE/KitWare — turbine blade, heat exchanger Andrew Willmott — radiosity solutionAndrew Willmott — radiosity solution

53. Available Online: Further Details & Free Stuff Free sample implementation, example surface models, example surface models, related papers. related papers. http://www.cs.cmu.edu/~garland/quadrics/http://www.cs.cmu.edu/~garland/quadrics/