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Resolving Surface Collisions through Intersection Contour Minimization Pascal Volino Nadia Magnenat-Thalmann MIRALab, University of Geneva SIGGRAPH 2006

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Abstract Advanced methods are need for CD To recovery intersecting surfaces Not rely on intersection regions More broader application Much simpler to implement

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Outline Introduction Related Work Description of the Method Results Conclusions

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Introduction

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Early CD for cloth are restricted for cloth and volumes Methods for ensuring adequate constrains are complex

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Related Work

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Not only prevent but also repair the intersections Common approach is to identify the “collision regions” by Volino et al.[1995] Retain a constant orientation with detection Impractical to implement

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Related Work Simpler approaches preventing surface intersections to occur or spread Baraff et al [2003] use “flypapering” Bridson et al [2003] preserve wrinkle patterns Bridson et al [2002] the most comprehensive way

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Related Work A major contribution by Baraff et al [2003] Global Intersection Analysis method Track intersections by identifying closed contour Establish orientation correspondence Apply collision response method Major restriction Necessity of closed intersection contour

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Related Work A major contribution by Baraff et al [2003] Global Intersection Analysis method Track intersections by identifying closed contour Establish orientation correspondence Apply collision response method Major restriction Necessity of closed intersection contour

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Goal To overcome these limitations Intersection region Non-consist constrains Impractical to implement Minimizing the length of the intersections contour Rather than spending time to identifying colliding surface regions

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Description of the Method Minimizing Edge-Polygon Intersections Integration with Collision response The local and the Global Scheme

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Description of the Method Resolution scheme Define a collision scheme that induce a relative displacement So as to reduce the length of the intersection contour disappearance of the surface intersection

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Minimizing Edge-Polygon Intersections

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Integration with Collision response Integrating the effects of collision in the simulation Defining an “interaction vector” H from the gradient G H should on the same direction of G Their norm should be related

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The local and the Global Scheme Sometimes not efficient if the contour is already quite straight or the actions are the largest on the region

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Results Some Test Examples Performance and Limitations

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Results Integrated in a cloth simulation engine Based on particle systems for accurate representation Broad-phase CD using AABB hierarchies Collisions are detected through edge-polygon intersections

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Some Test Examples Untangling Cloth Surfaces Local scheme works poorly in this context Between 0.4 and 0.2 sec per iteration

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Some Test Examples Robustness Test Randomly ignoring 50% of all collisions detected Local scheme is fairly efficient in this context

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Some Test Examples The Ribbon Simulation polygons of the ribbon, took roughly 3 to 30 sec per iteration Shear deformations often break the simulation

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Some Test Examples Garment Simulation Several layers of cloth Not always accurate

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Performance and Limitations The number of edge-polygon intersections remains very low Compared to the number of regular collisions between mesh elements Resolve intersections progressively along the simulation is more efficient

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Performance and Limitations In few configurations, the algorithm converges to a local minimum Combined with intersection region identify

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Conclusions

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The method is general and not suffer from the limitations of existing method Simple to implement The local scheme only relies on a simple geometrical computation The global scheme efficiently solve very large surface intersections easily be combined with most usual approaches for CD

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Question?

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