Geometry channel node

Uses a geometry object to choose a sop from which the channels will be created.

All

Parameters

Example files

See also: Export, Fetch, Image, Particle

The Geometry CHOP uses a geometry object to choose a SOP from which the channels will be created. The channels are created from the point attributes of a SOP, such as the X, Y and Z of the point position.

The SOP can select a subset of the points using Point Groups. The set of attributes that are converted to channels are chosen using the names of the attributes seen on the Info pop-up of SOP tiles.

See the Channel SOP

Note

This CHOP works in tandem with the Geometry > Channel SOP. Point data can be modified in CHOPs and then fed back to SOPs through the Channel SOP, therefore be sure to take a look at the Channel SOP description.

Parameters

Geometry

SOP

Retrieves the geometry from the SOP pointed to by this path.

Group

Fetch only the points within this point group. If blank, all points are fetched.

Method

The geometry fetch method.

Static	Creates one channel for each attribute, and all points use this channel (the first point resides at index 0, the next at 1, and so on). The length of the channels will be the number of points fetched.
Animated	Creates one channel per attribute per point. The channels show the animation of each point’s position/attribute values.

Attribute Scope

A string list of attributes to fetch from the SOP. The common attributes are:

P	point position (X, Y, Z) - 3 values.
Pw	point weight with a value of 1.
Cd	point color (red, green, blue) - 3 values.
Alpha	point alpha with a value of 1.
N	point normal value (X, Y, Z) - 3 values.
uv	point texture coordinates (U,V,W) - 3 values.

Rename Scope

The names to use for the newly fetched attributes. There must be one name per attribute, so an attribute scope of “P” should have a rename scope with three names (like tx ty tz).

Transform Object

If a transform object is specified, the point values will be represented relative to that object’s origin and rotation.

Organize by Attribute

(Applies to 'Animated Method' only) Will rebuild the fetched channels by the value of this attribute. A common example is the 'id' attribute found in particles. A channel is built for each unique id since the number of points may vary.

Channel

Start/End	The time range over which to fetch the geometry values when “Animated” Method is selected.
Sample Rate	The sample rate to use for the fetched channels.
Extend Left	The extend condition before the channel’s beginning.
Extend Right	The extend condition after the channel’s ending.
Default Value	The value of the default value extend condition.

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.

Example files

Geometry

$HFS/houdini/help/examples/nodes/chop/geometry/Geometry.cmd

Load | Launch

This is an example of how the Geometry CHOP can fetch data from a SOP and turn that data into channels.

In this case, the Geometry CHOP pulls in the position of every point in a Superquad SOP and creates channels from that data.

Usages in other examples

Example name	Example for
CopyStamping	Copy channel node	Load \| Launch
BlendPoseBasic	BlendPose channel node	Load \| Launch
ChannelSOPColorExample	Channel surface node	Load \| Launch
BlobbySphere	Channel surface node	Load \| Launch