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A Computationally Efficient Framework for Modeling Soft Body Impact

A Computationally Efficient Framework for Modeling Soft Body Impact. Sarah F. Frisken and Ronald N. Perry Mitsubishi Electric Research Laboratories. Modeling Soft Body Impact. Detect collisions between interacting bodies Model global motion changes (e.g., position and velocity)

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A Computationally Efficient Framework for Modeling Soft Body Impact

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  1. A Computationally Efficient Framework for Modeling Soft Body Impact Sarah F. Frisken and Ronald N. Perry Mitsubishi Electric Research Laboratories

  2. Modeling Soft Body Impact • Detect collisions between interacting bodies • Model global motion changes (e.g., position and velocity) • Apply a dynamic simulation method • Model local shape changes (i.e., deformation) • Apply a deformation method that may be • Non-physical (e.g. control point-based) • Physically plausible (e.g., FFD) • Physically realistic and dynamic (e.g. FEM)

  3. Modeling Soft Body Impact • Wide range of applications and goals • e.g., editing tools in Maya deform surfaces by moving nearby control points • e.g., computer simulation for games may approximate or exaggerate physics • e.g., protein docking for molecular modeling requires accurate modeling

  4. An Observation • Common requirements for modeling soft body interactions • Detect collisions between interacting soft bodies • Compute impact forces • Compute deformation forces and/or contact deformation

  5. A Proposal • Represent Objects with Adaptively Sampled Distance Fields (ADFs) • Compact representation of detailed shape • Efficient collision detection • Straightforward force computation • A means for estimating contact deformation

  6. Distance Fields • Specify the (possibly) signed distance to a shape -130 -95 -62 -45 -31 -46 -57 -86 -129 -90 -90 -49 -217 2516-3 -43 -90 -71 -5 30 -4 -38 -32 -3 -46 12 1 -50 -93 -3 -65 20 2D shape with sampled distances to its edge Regularly sampled distance values 2D distance field

  7. Distance Fields • Advantages • Provide trivial inside/outside and proximity tests for collision detection • Penalty-based contact forces can be computed for penetrating bodies using the distance field and its gradient • Implicit nature of the distance field provides a means for estimating contact forces

  8. Distance Fields • Disadvantages of regularly sampled distance fields • High sampling rates are required to representing objects with fine detail without aliasing • For regularly sampled volumes, high sampling rates require large volumes which are slow to process and render • Detail is limited by the fixed volume resolution

  9. Adaptively Sampled Distance Fields • Detail-directed sampling • High sampling rates only where needed • Spatial data structure (e.g., an octree) • Fast localization for efficient processing • Reconstruction method (e.g., trilinear interpolation) • For reconstructing the distance field and its gradient from the sampled distance values

  10. Advantages of ADFs ADFs provide • Spatial hierarchy • Distance field • Object surface • Object interior • Object exterior • Surface normal (gradient at surface) • Direction to closest surface point (gradient off surface) ADFs consolidate the data needed to represent complex objects

  11. Collision Detection Use ADF spatial hierarchy for efficient localization of potential collision

  12. Collision Detection • Collision occurs in the overlap region of the ADFs • Overlap region is determined using simple CSG operations • Full geometry of the overlap region is available • Can use the overlap region of ADF offset surfaces for proximity tests

  13. Contact Forces • Compute contact forces in the overlap region • Derive force vectors acting on penetrating body from distance field of the penetrated body Forces are computed in the overlap region

  14. Contact Forces • fV(p) =  dU(p) dU(p) • Compute contact forces • At surface points (shown here)OR • Over the entire overlap region (more accurate?) • Apply a deformation method (e.g. FEM) • Derive impact forces • From contact forces and surface normals • Apply a dynamic simulation method Deformation forces on the surface SV due to penetration of U by V

  15. Modeling Deformation using Implicit Functions • Approximate contact deformation by combining distance fields in the overlap region dU’(p) = min(dU(p),  dU(p) - (1 - ) dV(p)), (0,1)

  16. Modeling Deformation using Implicit Functions • Achieve different effects depending on method for combining distance fields Material compression with similar materials Material compression with V softer than U Volume preservation (after Cani, Graphics Interface ‘98)

  17. Summary • ADFs • Use distance fields to represent shape • Adaptive sampling provides efficient memory usage and reduced computation so we can represent very detailed shapes • Spatial data structure provides fast localization and processing • An efficient framework for soft body impact • Fast collision detection • Straightforward force computation • A means for estimating contact deformation

  18. Preliminary Results • Interactive computation and display of 2D contact forces Interactive force computation on complex shapes

  19. Preliminary Results • Can achieve detailed 3D contact deformation A soft sphere after impact with a ‘hard’ ADF model A soft sphere after impact with a ‘soft’ ADF model

  20. The End

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