Download - UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Some techniques to Speed up Collision Detection Yalmar Ponce Atencio LCG/PESC/COPPE.

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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