Houdini 21.0 Nodes Dynamics nodes

POP Steer Wander dynamics node

Applies forces to agents/particles to create random motion.

Since 14.0

This is a crowd behavior node, but you can also use it on regular particles (see the Output Attribute parameter).

This node has a Force parameter, which controls the base speed of the wander, and Amplitude, which controls the size of the changes to the base speed. For example, a high Force and low Amplitude results in fast motion with small deviations, while a low Force and high Amplitude results in a slower overall motion but with big swings in direction and speed.

Parameters

Activation

When turned off, this node has no effect. You can animate this to turn the behavior on or off at different times.

Group

Only modify certain groups out of all the agents/particles. You can name groups of agents using the Group Name parameter on the Crowd Source geometry node.

Output Attribute

Controls whether the node modifies the agent’s steerforce attribute (used by the crowd solver) or the particle’s force attribute (used by the POP solver). If you are working with agents, set this parameter to Crowds steerforce. If you are working with particles, set this parameter to POP force.

Weight

When Output Attribute is set to Crowd steerforce, this value is used by the crowd solver to normalize and scale multiple forces that apply to an agent.

Force

The base strength of the wander force.

Ignore Mass

When turned on, ignores any mass on the input particles.

Since forces are stored as force rather than accel (acceleration), this is done by multiplying the force by the mass attribute. This is then canceled out by the solver.

airresist is also similarly multiplied.

Ignoring mass ensures that small pieces of an RBD object move at the same speed as big pieces. This makes for a more controllable simulation.

Use VEXpressions

When turned on, uses a local expression to override specific parameters. Select from the drop-down menu on the right to see the variables that you can modify.

Noise

Type

Specifies whether to use 2D noise or 3D noise.

Amplitude

The size of the random changes to Force.

Swirl Size

The size of the noise pattern.

Swirl Scale

The spatial size of the noise field in X, Y, and Z.

Pulse Length

The duration of the lowest frequency in time.

Roughness

The scale of the noise added with each iteration.

Attenuation

The noise attenuation exponent.

Turbulence

The number of iterations of fractal noise to add.

Offset

The amount to shift the noise.

Use VEXpressions

When turned on, uses a local expression to override specific parameters. Select from the drop-down menu on the right to see the variables that you can modify.

Bindings

Geometry

The name of the simulation data to apply the POP node to. This is commonly Geometry, but POP networks can be designed to apply to different geometry if desired.

Evaluation Node Path

For nodes with local expressions, this controls where ch() style expressions in VEX are evaluated with respect to. By setting this to “.”, you can ensure that relative references work. It is important to promote this if you are embedding a node inside an HDA if you are also exporting the local expressions.

See also

Dynamics nodes