Using the Corridor Map Method for Path Planning for a Large Number of Characters

Roland Geraerts, Arno Kamphuis, Ioannis Karamouzas, Mark OvermarsMIG’08

Do We Need a New Path Planning Algorithm?

Robotics Virtual environments

Nr. Entities a few robots many characters

Nr. DOFs many DOFs a few DOFs

CPU time much time available little time available

Type path nice path natural path

Algorithms A*, roadmap-based, waypoint-based, …

A*, roadmap-based, waypoint-based, …

Goals

• Fast and flexible path planner• Real-time planning for thousands of characters

• Dealing with local hazards

• Natural paths• Smooth

• Short

• Keeps some distance to obstacles

• Avoids other characters

• …

Outline

• Corridor Map Method• Path variation• Obstacle avoidance• Crowd simulation• Coherent groups• Conclusions & future work

The Corridor Map Method

• Construction phase (off-line)• Create a system of collision-free corridors for the static obstacles• Extract the Generalized Voronoi Diagram

• If a path exists, then it can be found• All cycles are included• Corridors have maximum clearance

Sampled GVD Corridor Map: GVD + clearance info

The Corridor Map Method

• Construction phase (off-line)

McKenna MOUT environment Footprint and Corridor Map: 0.05s

The Corridor Map Method

• Construction phase (off-line)

City environment Footprint and Corridor Map: 0.64s

The Corridor Map Method

• Query phase (on-line)• Extract corridor for given start and goal provides global route

• The characters follows an attraction point provides local route

• Runs along backbone path toward goal

• Used to define a force function, applied to the character

• Path is obtained by integration over time while updating the

velocity, position, and attraction point of the character

• Yields a smooth (C1-continuous) path

• Other behavior: locally adjust path by adding forces

Query points Corridor andbackbone path

Path

The Corridor Map Method

• Query phase (on-line)

McKenna MOUT environment Corridor and path: 0.2ms (average)

The Corridor Map Method

• Query phase (on-line)

City environment Corridor and path: 1.2ms (average)

Path Variation

• Alternative paths for a character• Provides a less predictable opponent (in a game)

• May enhance the realism of the gaming experience

• Approach• Add a random force (bias) to the character

• Control the direction of the bias by e.g. Perlin Noise

100 random paths Lane formation Shorter path

Obstacle Avoidance

• Helbing and Molnar’s social force model; forces:• Acceleration toward the desired velocity of motion

• Repulsive forces from other characters and borders to keep some

clearance

• Attractive forces among characters

• We need efficient nearest neighbor computations• 2D grid storing the characters

Crowd Simulation

• Goal oriented behavior• Each character has its own long term goal

• A start and goal fixes a corridor

• When a character has reached its goal, a new goal will be chosen

• Wandering behavior• Each character makes local decisions

• Each character follows its attraction point

• When the attraction point reaches a vertex in the corridor map,

one of the outgoing edges is selected

Crowd Simulation

• Goal oriented behavior• Forces: standard force, biasing force, collision avoidance force

Crowd Simulation

• Goal oriented behavior• Forces: standard force, biasing force, collision avoidance force

Coherent Groups

• In a coherent group, characters stay close to each other• Group coherence is obtained by limiting

• The width of the corridor

• The extent along the corridor where the characters can move

Large width and area Small width, large area Small width and area

Coherent Groups

Conclusions

• The Corridor Map Method is fast• ~10,000 characters can be simulated in real-time

• The Corridor Map Method is flexible• Path variation

• Collision avoidance

• Crowds

• Coherent groups

• The Corridor Map Method produces natural paths• Smooth

• Short

• Keeps some distance to obstacles

• …