Object channel node

Compares two objects and returns information on their relative positions and orientations.

All Parameters Example files

See also: ObjectChain, Handle

The Object CHOP compares two objects and returns information on their relative positions and orientations. The information that can be output is:

The optional two inputs allow you to compare X,Y,Z points in world space with objects or each other. The inputs are expected to have three channels containing XYZ points. These inputs replace the target and/or reference objects. Object and points can be compared with each other, but “Rotation” mode will always return zero.

If either the target or reference objects (but not both) are missing, then the identity transform is used in place. This allows us to obtain the world transform of an object by only supplying a target object, or to obtain the inverse world transform of an object by only supplying the reference object.

Parameters

Object

Target Object

The object that is being compared to the reference object.

Name

Specify the target using a string.

Reference Object

The object that acts as the basis for the comparison.

Name

Specify the reference using a string.

Use Reference Bone Length

If enabled and the Reference Object is a Bone object, then the reference transform at the end of the bone will be used instead of at the beginning of the bone.

Compute

The information to output from the objects, as listed above.

Rotate Order

The rotation order to use for “Rotation” or “Bearing” computation.

Bearing Reference

Bearing requires a direction to use as a reference base.

Bearing Vector

An arbitrary base direction for /bearing x y z the bearing calculation.

Point Scope

When one of the optional point inputs is connected, this determines which channels represent X, Y and Z.

Channel

Channel Names

Sets how the output channels are named. A : is placed in the channel name where / is in the path.

Channel Name

Only use the name of the channel.

Target and Channel Names

Include the name of the target with the channel name, separated by a colon (:).

Reference and Channel Names

Include the name of the reference with the channel name, separated by a colon (:).

Sample Rate

The sampling rate of the channel in frames per second (Hz).

Channel Range

Indicates how much of the channel to fetch.

Use Full Animation Range

All of the animated range.

Use Current Frame

Only the sample at the current frame.

Use Start/End

Specify the range below.

Start

The start time of the desired interval of the object path.

End

The end time of the desired interval of the object path.

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.

Example files

ObjectBasic

$HFS/houdini/help/examples/nodes/chop/object/ObjectBasic.cmd

Load | Launch

This file demonstrates the Object CHOP.

The CHOP is used to bring in the channel information from a Object.

This data can then be manipulated within CHOPs and exported back into the Object, or even a different Operator.

Usages in other examples

Example name Example for
SimpleIKSolver

IKSolver channel node

Load | Launch