1. Simulating Virtual Human Crowds with a Leader-Follower Model Tsai-Yen Li, Ying-Juin Jeng, Shih-I Chang National Chengchi University Slides updated and presented by Vishal Srivastava Original slides by Romain Thibaux, Benson Limketkai

2. 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

4. Potential applications Virtual shopping in a 3D shopping mall Distributed networked games Simulation of a tour group

5. 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

6. 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

7. Planning for Two Leaders 1 2

8. 1 2

9. 1 2 Path is planned using artificial potential field

10. Planning for Two Leaders 1 2

11. Coordinated motions Solid circles mark leader positions Circle traces are planned paths Numbers indicate planning order Four snapshots…

12. Motion of the Followers Separation Cohesion Alignment Obstacles Leader Steering Forces

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

14. 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

15. 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

16. Example of Crowd Region Estimation

17. 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”

18. Screen shots

19. Concerns Is motion really human-like? Is planning too expensive for real applications?

20. 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