Anatomy of a Crowd Simulation

There are several models and nodes involved in creating a CrowdFX simulation.

Each of the letters on the nodes in this image corresponds to a description in the table below:

A	The original model (sometimes called the source model or actor source) is a polygon mesh object that is enveloped to a set of deformers, and has action sources (and optionally shape keys) defined for it in its Mixer node. See Preparing a Model for CrowdFX for a list of requirements for the model to be used with CrowdFX. Once you have created the crowd simulation, you can hide the original model by clicking the Show/Hide Actor Source button in the CrowdFX Actor Proxy Property Editor (D).
B	The Crowd model is created as soon as you select an actor to be used for CrowdFX (see Loading Actors for the Crowd Simulation). This model contains all the nodes that are required for a single crowd simulation. You can have multiple crowd simulations in a scene, but only one can be the current crowd (see Setting the Current Crowd). In the CrowdFX Property Editor, whose icon is directly below the Crowd model node, you can set this crowd as the current one, as well as cache the crowd simulation.
C	The Actors_Proxies node contains all the actor proxy models (D) that are used in this crowd simulation. You can use multiple actor proxies in each crowd simulation. In the CrowdFX Actors Proxies Property Editor, whose icon is directly below this node, you can access all actor proxies in the crowd. Here you can inspect each actor proxy's animation or rig, as well as add actors to, or remove them from, the simulation. Choose the CrowdFX Actors Inspect Actor Proxies command on the ICE toolbar to open this property editor.
D	An actor proxy model (sometimes called the actor model or just actor) is a node that contains a copy of the original model's mesh (A). All other elements that are required for this actor proxy for CrowdFX are contained within this model. A proxy model is created for each original model that you select to be in the crowd simulation - in this case, it's a proxy of the original AstroMan model. In the CrowdFX Actor Proxy Property Editor, whose icon is directly below this node, you can manage the actor proxy, such as selecting the actions that the actor proxy will use in the crowd simulation, as well as other tasks.
E	The Animation Proxies node contains a point cloud for each of the action sources loaded for the actor proxy. The local transform data that was in each action source is stored in the point cloud as global transform data on every deformer in the rig proxy (F) at each frame of animation. The point clouds also set certain ICE attributes on the actions so that they can be used in the ICE trees for the crowd simulation.
F	The Rig Proxy is a copy of the original model's rig, but includes only its deformers - any other part of the original rig is not copied. This rig is the one used to deform the actor proxy in the crowd simulation. You can make changes to the hierarchy or create constraints on the rig proxy without affecting the original model's rig or animation - see Modifying the Actor's Rig for more information. To see the rig proxy, click the View Rig button in either the CrowdFX Actor Proxy Property Editor or CrowdFX Actors Proxies Property Editor.
G	The Actor Copies polygon mesh is a single mesh that includes all instances of an actor's mesh in the crowd simulation. This is normally the actor instance geometry that you see in the viewport. See Viewing the Actor's Envelope for more information. You can toggle the visibility of the Actor Copies mesh of the current crowd with the CrowdFX Crowd Edit Show/Hide PolyMesh Copies command on the ICE toolbar.
H	The Mesh Proxies polygon mesh is a copy of the original model's mesh. It's hidden by default, but you can display it in an OpenGL display mode using a realtime skinning shader. See Viewing the Actor's Envelope for more information
I	The Skeletons Cloud point cloud stores data for the actor proxy and is hidden by default. It contains the Create Actor Cloud ICE tree in the Modeling region that gets data from the crowd simulation point cloud (L), and stores information about each instance of the actor in the simulation, such as its global point position, envelope deformation information, shape key, and Actor ID.
J	The Deformer Proxies group contains references to all the deformers in the actor's Rig Proxy (F). Having the deformers in a group makes it easier to access them because they're displayed in a flat list, and not nested as they are in a hierarchy.
K	The Simulation node contains data related to the emitters, goal objects, walls (obstacles), and the point cloud (L) that drives the crowd simulation. The Emitters_Root null contains the geometry for each directional emitter you draw in the crowd simulation - see Crowd Particle Emitters. The Walls_Root null contains the geometry for each wall created in the crowd simulation - see Avoiding Collisions with Obstacles (Walls). The Goals_Root null contains the geometry for each goal object created in the crowd simulation - see Moving Toward Goals.
L	The Point_Cloud is the point cloud that drives the crowd simulation. It has several ICE trees in it, as described in Creating the Crowd Particle Simulation. Choose the CrowdFX Simulation Select Simulation Cloud command to select this point cloud.
M	These groups contain references to objects in various parts of the Crowd model. They make it easy to find similar elements that belong to this crowd simulation.