UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Some techniques to Speed up Collision Detection Yalmar Ponce...

UNIVERSIDADE FEDERAL DO RIO DE JANEIRO

Some techniques to Speed up Collision Detection

Yalmar Ponce Atencio

LCG/PESC/COPPE


Problem

Given a large environment with moving objects,

Detect overlapping objectsOverlapping triangles in each pair


Goal

Interactive collision detectionbetween complex objects

Large number of objectsHigh primitive count Non-convex objectsOpen and closed objectsDeformable objects•Changing topology


Related Work

Collision detectionHardware accelerated techniquesObject space techniquesTwo phases

Broad phase – Compute object pairs in close proximity Narrow phase – Check each pair for exact collision detection


Related WorkBroad phase

Spatial partitioningSweep-and-prune

Narrow phaseSpatial partitioningBounding volume hierarchies

Surveys [Klosowski 1998, Lin and Manocha 2003, Redon et al. 2002, Andrew Nealen et al. 2005]


Limitations of Object-space Techniques

Considerable pre-processingHard to achieve real-time performance on complex deformable models


Collision Detection using Graphics Hardware

Primitive rasterization – sorting in screen-space

Interference tests• NV_OCCLUSION_QUERY• Requires high screen resolution


Image Space TechniquesUse of graphics hardware

CSG rendering [Goldfeather et al. 1989, Rossignac et al. 1990]Interferences and cross-sections [Baciu et al. 1998, Myszkowski 1995, Rossignac et al. 1992, Shinya and Forgue 1991]Virtual Surgery [Lombardo et al. 1999]Minkowski sums [Kim et al. 2001]Cloth animation [Vassilev et al. 2001]Proximity computation [Hoff et al. 2001, 2002]CULLIDE, R-CULLIDE, Q-CULLIDE[Govindaraju et al. 2003-2005]


Limitations of Current Approaches

Closed modelsFrame buffer readbacks – slow


Outline

OverviewPruning AlgorithmHashedOctreeImplementation and ResultsConclusions and Future Work


Outline

OverviewPruning TechniquesHashedOctreeImplementation and ResultsConclusions and Future Work


Overview

Potentially Colliding Set (PCS) computationExact collision tests on the PCS using a HashedOctree


Technique

Object LevelPruning

Sub-objectLevel

PruningExact Tests

GPU based PCS computation

Using CPU


Potentially Colliding Set (PCS)

PCS

Scene


Outline



Pruning Techniques

Occlusion queriesBack-face culling

Convex modelsView volume culling

glSelectBuffer()


View volume culling

Using AABBs


A

B

Improvements

Using OBBsTransform B for A orientationUse OBBB as cliping planesPCSB


Outline



CreationHierarchical• Recursively

Hash [N.A.Gumerov et al. 2003]• From hierarchical

Octree or Using a generated Key

• Key is generated from parent nodes

• Hash table uses k mod 2b (b last bits)

Octree x HashedOctree

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Search in Octree

p

Hierarchicalrecursive


Search in HashedOctree

p

Direct accessUsing key node


Outline



HashedOctree

Morton keyGenerated recursivelyKey is computed using Interleaving• k(n) = xlylzlxl-1yl-1zl-1…x1y1z1

• l is the level of the octreeInterleaving is achieved by “OR”ing


B

A

Potentially Colliding Setx HashedOctree

Each object have a HashedOctree

PCSB = trgls_in(OBBA OBBB)

Exact test PCSB x HashedOctreeA


Algorithm

CSA = CSB = foreach (tB in PCSB){ PCSA = foreach (p in tB) PCSA HashedOctreeA.searchElems(p) if (PCSA ) foreach (tA in PCSA) if (tA tB){ CSA tA

CSB tB }}


Results


Results

Tests on a Pentium M 2.0Ghz with ATI X600 128Mb PCIe and 1Gb RAM

Hierarchical Octree

Depth Level 10

Hashed Octree Depth Level

10

Search a Point

Cow 4315 Triangles 8626 Faces

9-11 us 4-4.5 us

Dragon 48581 Triangles 93286 Faces

14-19 us 4-4.9 us

Exact intersection Triangle-Triangle

Torus x Torus632 Triangles 1264 Faces

12-120 us 5-39 us

Cow x Torus 45-390 us 15-99 us


Outline



Conclusions and Future Work

ConclusionsEarlier image based collision detection approaches present some limitations (Screen Resolution).Object level Pruning and Sub-object pruning are required.Hashed Octree reduces a query up to 80% over hierarchical Octree.

Future WorkGeometric models can be mapped efficiently on images (Geometry Images).Geometry images allow to generate Octrees and volume hierarchies in real-time on current GPUs.


Thanks all folks!


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UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Some techniques to Speed up Collision Detection Yalmar Ponce...

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