Particle channel node

Produces translate and rotate channels to move Objects according to the positions of particles in a POP Network.

This CHOP produces translate and rotate channels to move Objects according to the positions of particles in a POP Network. Channels are generated for all particles with an instance attribute and which have the override state turned on.

Parameters

Particle

POP Path	POP to cook.
Method	Specifies whether the CHOP should generate channel values for the current frame (Dynamic) or for all frames at once (Cached).
Extract Scope	Specifies a mask of channels to generate.
Update	Forces an update of the CHOP if it is in Static mode.

Standard

Start Time	Time at which simulation starts
Preroll Time	At start time, simulation has already been running this long
Initial State	Geometry to use as initial state of simulation
Random Seed	This value is used to initialize the pseudo-random sequence used by the simulation. It is useful for generating different simulations from the same network.
Oversampling	How many times to cook in between frames
Max # of Particles	Controls the maximum number of particles that can exist in the simulation at any given moment. A value of 0 means particles can always be birthed.
Remove Unused Points	Remove the points associated with dead particles. This can reduce the memory footprint of the simulation. On the other hand, disabling this option can improve performance by recycling points. Changing this option can affect the point numbers associated with individual particles.

Input Geo

SOP N

The path to a SOP to use as Context Geometry N.

The display or render SOP can be specified using paths of the form object_path/display_sop or object_path/render_sop, respectively.

Channel

Start, End	The start time of the channels.
Sample Rate	The sample rate of the channels.
Extend Left	The left extend conditions.
Extend Right	The right extend conditions.
Default Value	The default value for extend conditions.

Common

Some of these parameters may not be avaiable on all CHOP nodes.

Scope

To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example * (match all), and ? (match single character).

The following are examples of possible channel name matching options:

`chan2`	Matches a single channel name.
`chan3 tx ty tz`	Matches four channel names, separated by spaces.
`chan*`	Matches each channel that starts with `chan`.
`foot`	Matches each channel that has `foot` in it.
`t?`	The `?` matches a single character. `t?` matches two-character channels starting with t.
`r[xyz]`	Matches channels `rx`, `ry` and `rz`.
`blend[3-7:2]`	Matches number ranges giving `blend3`, `blend5`, and `blend7`.
`blend[2-3,5,13]`	Matches channels `blend2`, `blend3`, `blend5`, `blend13`.
`t[xyz]`	`[xyz]`matches three characters, giving channels `tx`, `ty` and `tz`.

Sample Rate Match

The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.

Resample At First Input’s Rate	Use rate of first input to resample others.
Resample At Maximum Rate	Resample to highest sample rate.
Resample At Minimum Rate	Resample to the lowest sample rate.
Error if Rates Differ	Does not accept conflicting sample rates.

Units

The units for which time parameters are specified.

For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).

Note

When you change the Units parameter, it does not convert the existing parameters to the new units.

Time Slice

Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.

Unload

Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.

Export Prefix

The Export prefix is prepended to CHOP channel names to determine where to export to.

For example, if the CHOP channel was named geo1:tx, and the prefix was /obj, the channel would be exported to /obj/geo1/tx.

Note

You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as obj:geo1:tx.

Graph Color

Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.

Graph Color Step

When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.

Usages in other examples

Example name	Example for