Channel surface node

Reads sample data from a chop and converts it into point positions and point attributes.

All Parameters Example files

This node is complementary to the Geometry CHOP. The Channels created by the Geometry CHOP can be modified and then re-inserted into the op network via a Channel SOP.

This does what a Point SOP with a chopci() function can do, but is much faster.

By using point groups from the incoming op, the channels can be inserted only into the group’s points.

When you want one component of an array, like the Y value of the point position, you need to put P(1) into the Attribute Scope.

Parameters

Group

Modify only the points within this point group. If blank, all points are modified.

CHOP

Retrieves the sample data from this CHOP.

Method

The sample data fetch method.

Static

Uses 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 should be at least the number of points modified.

Animated

Uses one channel per attribute per point. The channels show the animation of each point’s position/attribute values.

Channel Scope

The names to use for the newly modified attributes. There must be one name per attribute (eg. an attribute scope of “P” should have a channel scope with three names: tx ty tz).

Attribute Scope

A string list of attributes to modify. For only one component of an array, such as the Y value of the point position, specify the number of elements in brackets (in this case, P(1) would be used).

The common attributes are:

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

Organize by Attribute (Applies to 'Animated Method' only)

Will reorganize 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.

Example files

BlobbySphere

$HFS/houdini/help/examples/nodes/sop/channel/BlobbySphere.cmd

Load | Launch

This is a simple example of how to utilize the Channel SOP to bring information from CHOPs into SOPs and apply it to geometry.

We use an animated sphere and create a lag in the animation of selected areas of the sphere.

In a CHOP network, the Geometry CHOP brings in point position data of the sphere geometry and runs it through a Lag CHOP for the delaying effect. The Channel SOP then references the Lag CHOP and applies the point data back to the selected areas of the original NURBS sphere.

ChannelSOPColorExample

$HFS/houdini/help/examples/nodes/sop/channel/ChannelSOPColorExample.otl

Load | Launch

This example demonstrates using CHOPs to drive geometry color values via the Channel SOP.

ChannelSoftbody

$HFS/houdini/help

Load | Launch

This is an Advanced example.

This network contains example of how the Channel SOP can be used in conjunction with a POP network to manipulate geometry at the SOP level.

First a simple particle network allows the creation and collision of particles sourced from grid geometry.

Next the positional data of the particles is evaluated through a CHOP network using a Geometry CHOP. The Geometry CHOP returns the tx, ty and tz values for every particle birthed in the POP network.

Then, a Channel SOP brings the positional data back to the geometry level and applies it to the points on the original grid surface.

Usages in other examples

Example name Example for
CopyStamping

Copy channel node

Load | Launch

BlendPoseBasic

BlendPose channel node

Load | Launch