I-COLLIDE: An Interactive and Exact System

for Large-Scale Environments



Jonathan D. Cohen Ming C. Lin Dinesh Mano cha MadhavK.Ponamgi

Department of Computer Science

University of North Carolina

Chap el Hill, NC 27599-3175

fcohenj,lin,mano cha,p [email protected]

ABSTRACT: or grasp ed. Such actions require accurate collision detec-

We present an exact and interactive collision detection tion. However, there maybehundreds, even thousands

system, I-COLLIDE, for large-scale environments. Such of ob jects in the virtual world, so a brute-force approach

environments are characterized by the numb er of ob jects that tests all p ossible pairs for collision s is not acceptable.

undergoing rigid motion and the complexity of the mo d- Eciency is critical in a virtual environment, otherwise

els. The do es not assume the ob jects' motions its interactive nature is lost [24]. A fast and interactive

can b e expressed as a closed form function of time. The collision detection algorithm is a fundamental comp onent

collision detection system is general and can b e easily in- of a complex virtual environment.

terfaced with a variety of application s. The algorithm

The ob jective of collision detection is to rep ort all geo-

uses a two-level approach based on pruning multiple-

metric contacts b etween ob jects. If we know the p ositions

ob ject pairs using b ounding b oxes and p erforming exact

and orientations of the ob jects in advance, we can solve

collision detection b etween selected pairs of p olyhedral

collision detection as a function of time. However, this

mo dels. We demonstrate the p erformance of the system

is not the case in virtual environments or other interac-

in walkthrough and simulation environments consisting

tive applications. In fact, in a walkthrough environment,

of a large numberofmoving ob jects. In particular, the

we usually do not haveany information regarding the

system takes less than 1=20 of a second to determine all

maximum velo city or acceleration, b ecause the user may

the collisio ns and contacts in an environment consisting

move with abrupt changes in direction and sp eed. Due to

of more than a 1000 moving p olytop es, each consisting of

these unconstrained variables, collision detection is cur-

more than 50 faces on an HP-9000/750.

rently considered to b e one of the ma jor b ottlenecks in

building interactive simulated environments [20].

1 INTRODUCTION

Main Contribution: We present a collision de-

Collision detection is a fundamental problem in computer

tection algorithm and system for interactive and exact

animation, physically -based mo deling, computer simu-

collision detection in complex environments. In contrast

lated environments and rob otics. In these applications ,

to the previous work, we show that accurate, interac-

an ob ject's motion is constrained by collisio ns with other

tive p erformance can b e attained in most environments if

ob jects and by other dynamic constraints. The prob-

we use coherence to sp eed up pairwise interference tests

lem has b een well studied in the literature. However, no

and to reduce the actual numb er of these tests we p er-

2

go o d general collision detection and systems

form. We are able to successfully trim the O n  p os-

are known for interactive large-scale environments.

sible interactions of n simultaneousl y moving ob jects to

A large-scale virtual environment, likeawalkthrough,

O n + m where m is the numb er of ob jects very close

creates a computer-generated world, lled wi