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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.
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 available on all CHOP nodes.
Scope
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in 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.
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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the 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 of the time parameters.
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, the existing parameters are not converted to the new units.
Time Slice
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the 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 to it for display in the graph, but you can override the color with the 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.
Examples ¶
ObjectBasic Example for Object channel node
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.
See also |