= How to |> set up a crowd simulation =

Crowd simulations usually consist of a particle system with instanced geometry (such as people or animals). A POP Network is set up to control the way the instanced geometry moves and interacts with each other in the scene. 

* Start by creating a particle system using either the [Source from Geometry|/shelf/emitfromgeometry] or [Emitter|/shelf/emitfromlocation] tool on the __Create Particles__ shelf.

* Apply a directional [force|Node:pop/force] to the particles.

* [Instance|Node:pop/instance] geometry onto the points.

* Control the behavior of particles when they collide with geometry using a [Collision|Node:pop/collision] node.

* Use a [Soft Limit|Node:pop/softlimit] particle node to create a boundary with spongy bounces. This POP provides smoother, less jerky bounces than the [Limit|Node:pop/limit] and [Collision|Node:pop/collision] POPs.

* Add an [Interact|Node:pop/interact] node to make the particles attract or repel each other.

* Set the velocity of the particles with a [Velocity|Node:pop/velocity] particle node.

* Insert a [Speed Limit|Node:pop/speedlimit] particle node to set a minimum and maximum velocity for the particles.

* Apply some drag to the velocity of the particles by using the [Drag|Node:pop/drag] tool.

* Add an [Attractor|Node:pop/attractor] node to attract or repel the particles toward/away from a force defined by a [Force SOP|Node:sop/force] (for metaballs) or the Force tab of a [Point SOP|Node:sop/point] (for other geometry types).

[Anim:/images/howto/mice.gif]

This example shows a particle simulation with toy mice instanced onto the points.