1. Crowd Simulation (INFOMCRWS) - Introduction to Crowd Simulation
Wouter van Toll
November 15, 2017

2. INFOMCRWS: Introduction to Crowd Simulation
Contents
Recap
Path planning and navigation meshes
Overview of crowd simulation research
Multi-level crowd simulation
Other topics
Open problems
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

3. Recap Path planning and navigation meshes November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

4. INFOMCRWS: Introduction to Crowd Simulation
Virtual environment (3D)
Crowd simulation (often 2D)
Fancy visualization (3D)
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

5. Crowd simulation Many applications (entertainment + serious)
Large crowds  Many queries
We want real-time performance
Planet Coaster (Frontier)
Grand Depart 2015 (Movares),
using our software
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INFOMCRWS: Introduction to Crowd Simulation

6. Region-based path planning
Navigation mesh
Many spatial subdivisions exist
Grids are easiest, but imperfect
Coverage, connectivity, storage
= Regions + (Dual) Graph
Trapezoidal map
Triangulation
Grid
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

7. Region-based path planning
Query
 Sequence of regions
 Indicative route (via funnel algorithm)
Simulation loop
 Shortest path in the graph
Q: Shortest path?
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INFOMCRWS: Introduction to Crowd Simulation

8. INFOMCRWS: Introduction to Crowd Simulation
Path planning in games
Trend
Graphs, grids  Navigation meshes
Manual  Automatic
Static  Dynamic
Increasingly large crowds
Typical errors
Incorrect graphs
Unnatural paths
Poor response to dynamic updates
Insufficient local methods / collision avoidance
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

9. Overview of crowd simulation methods
Towards an
Overview of crowd simulation methods
A Generic Categorization of Research Areas
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

10. Overview (1/6) Path planning Algorithms: Data structures:
A*, Dijkstra, ...
Data structures:
Navigation meshes, grids, ...
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

11. Path planning – Examples
Shortest path
Other criteria
Funnel
algorithm:
Shortest path
from a corridor
Density-based (van Toll et al., 2012)
Stealth-based (Schager & Geraerts, 2010)
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INFOMCRWS: Introduction to Crowd Simulation

12. Overview (2/6) Path planning Local movement Algorithms:
A*, Dijkstra, ...
Data structures:
Navigation meshes, grids, ...
Local movement
(“steering”)
Collision
avoidance
Groups, coherence,
social rules, ...
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

13. Local movement: Examples
Social forces
(Helbing & Molnár,
1995)
Flocking (Reynolds, 1987)
Velocity obstacles
(van den Berg et al., 2009+)
Vision-based collision avoidance
(Moussaïd et al,
2010)
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INFOMCRWS: Introduction to Crowd Simulation

14. Local movement: More examples
Streams (van Goethem
et al., 2015)
Social groups (Kremyzas et al., 2016)
Coherent groups (Kamphuis & Overmars, 2004)
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INFOMCRWS: Introduction to Crowd Simulation

15. Overview (3/6) Path planning Indicative route Path following
Algorithms:
A*, Dijkstra, ...
Data structures:
Navigation meshes, grids, ...
Indicative route
Path following
Local movement
Collision
avoidance
Groups, coherence,
social rules, ...
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

16. Intermezzo: Weighted regions
What if the environment is more complex than “walkable + obstacles”?
Polygonal areas with (personal) costs
Find minimum-cost path?
Unsolvable in the Algebraic Computation Model over the Rational Numbers
Approximation algorithms
Path following
MIRAN (Jaklin et al., 2013)
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INFOMCRWS: Introduction to Crowd Simulation

17. INFOMCRWS: Introduction to Crowd Simulation
Overview (4/6)
Visualization
Path planning
Animation
Rendering
Path following
Local movement
Simulation loop
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

18. INFOMCRWS: Introduction to Crowd Simulation
Overview (5/6)
High-level planning
Path planning
Modelling
Logic:
BDI, rules, memory, ...
Path following
Fixed
steps
of 0.1 s
Local movement
Simulation loop
As fast
as possible
Visualization
Animation loop
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

19. INFOMCRWS: Introduction to Crowd Simulation
Overview (6/6)
High-level planning
Path planning
Path planning
Path following
Path following
Local movement
Local movement
Visualization
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

20. INFOMCRWS: Introduction to Crowd Simulation
Multi-level planning
Advantages?
Split a big problem into simpler components
Mix and match various algorithms
Different behaviour per character
Disadvantages?
Choices in one level affect behavior in lower levels
When to reconsider these choices? (e.g. re-planning)
Path planning
Path following
Local movement
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

21. Alternative: Potential field
Continuous field of forces
Goal attracts, obstacles repel
Follow the direction of steepest descent
Common implementation: Grid
In case of moving characters (obstacles): update potential field each frame
Robot motion planning
(Latombe, 1991)
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

22. Alternative: Potential field
Advantages
Unifies global and local movement
Re-usable for similar characters
Good for high-density crowds
Disadvantages
Grid implementation
Different potential field for each goal / each character type
Local minima
Can be avoided, but (even) more expensive
Treuille et al., 2006
Narain et al., 2009
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

23. INFOMCRWS: Introduction to Crowd Simulation
Other topics
A mixed bag
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

24. Coordination and re-planning
Linear programming
(Karamouzas et al., 2013)
Dynamic updates + visibility-based re-planning (van Toll et al., 2015)
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

25. Moving through a dense crowd
Find a path that uses gaps between characters
Global becomes local?
Torso crowds
(Stüvel et al., 2015)
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INFOMCRWS: Introduction to Crowd Simulation

26. INFOMCRWS: Introduction to Crowd Simulation
Multi-threading
In a simulation step, many characters do “the same thing” at the same time
Allows parallel programming
GPU: thousands of tasks at the same time
Advantage: performance
Disadvantage (GPU):
What about rendering?
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

27. Evaluation How to compare different methods? Generic definitions
Objective quality metrics
Scenarios that cover the problem space
Conclusions(?)
SteerBench (Singh et al., 2009)
A comparative study of navigation meshes (van Toll et al., 2016)
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INFOMCRWS: Introduction to Crowd Simulation

28. INFOMCRWS: Introduction to Crowd Simulation
Evaluation
How to prove that a simulation is close to reality?
Compare to reality!
...but how?
Individual trajectories
Global trends
Density/speed relation
When is a conclusion general enough?
Lerner et al., 2009
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INFOMCRWS: Introduction to Crowd Simulation

29. INFOMCRWS: Introduction to Crowd Simulation
Closing comments */
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

30. INFOMCRWS: Introduction to Crowd Simulation
Summary
Path planning
Local movement
Path following
Visualization
High-level planning
Coordination, re-planning
or:
Potential fields
Multi-threading / GPU
Evaluation
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

31. INFOMCRWS: Introduction to Crowd Simulation
Remaining challenges
Navigation: see previous lecture
Problems within this paradigm
Reconsider global paths due to local hazards
High-level coordination
Long-term goals
Reliable validation
Human-like simulation for any scenario?
Huge crowds (≥1M) in real-time
Crowd prediction during a real-time event
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

32. INFOMCRWS: Introduction to Crowd Simulation
Next time
Explanation of our crowd simulation software
Tutorial to get started with Assignment 2
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation

33. Preparation for next time
If you haven’t done so yet...
Choose a non-taken paper (1-20) to present
Form teams for Assignments 1 and 2
Prepare for the tutorial
Bring a (Windows) laptop!
Install Unity
Read up on basic Unity usage
See website
November 18, 2018
INFOMCRWS: Introduction to Crowd Simulation