POP Advect by Filaments dynamics node

Uses vortex filaments to move particles.

On this page	Parameters Parameters Bindings Inputs Outputs Locals Examples
Since	13.0

This node swirls particles around vortex filaments. The Source Filaments imports filament geometry into the network. The Filament Solver advects the points of the filament curves to create motion. This node then uses the velocity field created by the moving vortex filaments to move particles.

See the filaments page for more information.

This node modifies the force, airresist, targetv, vel, and P attributes.

Parameters ¶

Activation

Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.

Note

This is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.

Group

Only affect a group of points (created with, for example, a Group POP or Collision Detection POP) out of all the points in the current stream.

Guide

If turned on, shows the guide geometry for this node.

Note

Even if the guide geometry is turned on here, it can be turned off by using the Hidden flag on the DOP node.

Parameters ¶

Filament Source

The source of the vortex filament curves. The context geometry refer to the inputs of this DOP Network.

SOP

The SOP path which contains the vortex filament curves.

DOP Object

The name of a DOP Object in the same simulation as this.

DOP Data

The sub-data path for the geometry in the DOP object.

Velocity Scale

A uniform scale to apply to the velocity field defined by the vortex filaments before any of the force applications.

Advection Type

There are several different ways to update a particle system in response to an external velocity field. They are broadly categorized as Force, Velocity, and Position updates.

Update Force

Adjusts the acceleration of the particles according to the force scale and the velocity field. This acts like the Force POP.

Update Velocity

Directly changes the velocity of the particles by blending in the velocity field, causing them to swiftly match the velocity field.

Update Position

Directly moves the particle positions. This is useful as it allows the particles own velocity to be considered independently of the bulk fluid velocity. This is similar to what the Gas Advect DOP would perform.

Treat as Wind

Rather than treating the computed force as an amount of force to add to the particle’s velocity, treat it as a wind speed to be matched by the particle. This causes the particle to be dragged to the goal speed, avoiding overshoot.

Force Scale

Scales the force when Treat as Wind is disabled.

Air Resistance

How strong of an influence to have on the particle. Higher values will cause it to match the wind velocity faster. This is also used to do a weighted average when competing winds are applied to the same particle.

Velocity Blend

In Update Velocity mode, the amount to mix in the field velocity every timestep.

Velocity Update

In Update Position mode it is possible to read in the velocity from the velocity field.

Note

The resulting velocity will be used by the particle integrator, so unless something special is done, this could result in double-moving the particle.

Bindings ¶

Geometry

The name of the simulation data to apply the POP node to. This commonly is 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 making this ., you can ensure 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.

Inputs ¶

First Input

This optional input has two purposes.

First, if it is wired to other POP nodes, they will be executed prior to this node executing. The chain of nodes will be processed in a top-down manner.

Second, if the input chain has a stream generator (such as POP Location, POP Source, or POP Stream), this node will only operate on the particles in that stream.

Outputs ¶

First Output

The output of this node should be wired into a solver chain.

Merge nodes can be used to combine multiple solver chains.

The final wiring should go into one of the purple inputs of a full-solver, such as POP Solver or FLIP Solver.

Locals ¶

channelname

This DOP node defines a local variable for each channel and parameter on the Data Options page, with the same name as the channel. So for example, the node may have channels for Position (positionx, positiony, positionz) and a parameter for an object name (objectname).

Then there will also be local variables with the names positionx, positiony, positionz, and objectname. These variables will evaluate to the previous value for that parameter.

This previous value is always stored as part of the data attached to the object being processed. This is essentially a shortcut for a dopfield expression like:

dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)

If the data does not already exist, then a value of zero or an empty string will be returned.

DATACT

This value is the simulation time (see variable ST) at which the current data was created. This value may not be the same as the current simulation time if this node is modifying existing data, rather than creating new data.

DATACF

This value is the simulation frame (see variable SF) at which the current data was created. This value may not be the same as the current simulation frame if this node is modifying existing data, rather than creating new data.

RELNAME