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The Object CHOP compares two objects and returns information on their relative positions and orientations. The information that can be output is:
Position of one object relative to another.
Rotation of one object relative to another.
Bearing of one object relative to another.
Single Bearing Angle between two objects.
Distance between the origin of two objects.
Inverse Square of the Distance between two objects.
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.
The object that is being compared to the reference object.
Specify the target using a string.
The object that acts as the basis for the comparison.
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.
The information to output from the objects, as listed above.
The rotation order to use for “Rotation” or “Bearing” computation.
Bearing requires a direction to use as a reference base.
An arbitrary base direction for /bearing x y z the bearing calculation.
When one of the optional point inputs is connected, this determines which channels represent X, Y and Z.
Sets how the output channels are named. A : is placed in the channel name where / is in the path.
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 (:).
The sampling rate of the channel in frames per second (Hz).
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.
Specify the range below.
The start time of the desired interval of the object path.
The end time of the desired interval of the object path.
The left extend conditions.
The right extend conditions.
The default value for extend conditions.
Some of these parameters may not be available on all CHOP nodes.
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:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
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.
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).
When you change the Units parameter, it does not convert the existing parameters to the new units.
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.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
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
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
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.