Simulating Virtual Human Crowds with a Leader-Follower Model

Tsai-Yen Li, Ying-Juin Jeng, Shih-I ChangNational Chengchi University

Slides updated and presented by Vishal SrivastavaOriginal slides by Romain Thibaux, Benson Limketkai

Problem Goal is to simulate the behavior of

crowds of people A crowd must navigate an

environment with: Obstacles Other moving crowds

Incredibly high degrees of freedom

Potential applications Virtual shopping in a 3D shopping

mall

Distributed networked games

Simulation of a tour group

Crowds Crowds contain one “leader” and

many “followers” Given a goal, the leader is in charge

of planning motions for its group Followers follow the leader closely as

it moves toward its goal

General Approach Decoupled planning approach

Paths executed by other leaders become the motion constraint for the current leader

Path planner estimates the shape and space of each group

Motion for followers is determined by artificial steering forces

Planning for Two Leaders

1

2

1

2

1

2

Path is planned using artificial potential field

Planning for Two Leaders

1

2

Coordinated motions

Solid circles mark leader positions

Circle traces are planned paths

Numbers indicate planning order

Four snapshots…

Motion of the Followers

Separation

Cohesion

Alignment

Obstacles

Leader

Steering Forces

Local Minima

Solution: Modify the attractive force to the leader’s last seen location.

Model the shape of crowds Treat each crowd as an object with

variable shape Estimate the shape Extend in CT-space when planning

Motion Planning For Crowds

Crowd Region Estimation Leader’s path

forms an axis Draw a half-circle

with diameter D behind the leader

Sweep the half-circle backward along the axis until it can accommodate all the followers

Example of Crowd Region Estimation

Implementations and Experiments

Stand-alone simulation module in Java

128 x 128 grid “planning time … is usually

fractions of a second” “planning times … are 500ms and

2000ms … on a low-end PC”

Screen shots

Concerns Is motion really human-like?

Is planning too expensive for real applications?

Summary

A planning system for generating coordinated motion for multiple crowds

Planner features: Crowd shape estimation module Integrated view of crowd motion planning

Applications in shared virtual environments and computer animation