|On this page|
This CHOP performs channel interpolation using an example-based method. Each example is taken from the pair of samples provided from the source and input channels. The data from the first input is then interpolated such that (as much as possible), the the target values will be obtained if the input values match the source values.
The first input specifies the channels used for the interpolation.
The second input specifies the source channels. This must contain the same number of channels as the first input.
The third input specifies the target channels. Each sample here is paired with the corresponding sample in the source channel. Thus, the length in samples of this input must matched with the second input. However, a different number of channels from the second input is allowed.
Radial Basis Functions
This class of interpolants provide smooth results that will likely match the example data.
This interpolant will create a plane of best fit. The results will likely not match the example data.
If enabled, this will clamp the input data to the corresponding value range of the source input before interpolating.
Best Fit Extrapolation
If enabled, a best fit method will be used for the extrapolation of data outside of the source inputs.
Maximize Best Fit
This option is only used when Best Fit Extrapolation is enabled. Turning this on will first maximize the interpolation using the plane of best fit, and then interpolate the remaining differences using the radial basis functions. This gives closer fits to the hyperplane method especially for kernel functions that specify a falloff. For those kernel functions, turning this option will also result in faster cooking. This option can give better results when there is high spatial correlation in the examples.
This specifies the kernel function used for the Radial Basis Functions interpolant. Different kernel functions will result in varying fits.
Specifies the exponent used for the Thin Plate kernal function. Larger values will give smoother results.
Specifies the fall off factor for the Gaussian, Multiquadric, Inverse Multiquadric, and Exponential Bump kernel functions. Larger values will give smoother results.
Specifies the solver method used for the interpolation.
The Cholesky solver is faster but not as stable.
The SVD solver is slower but will produce the higher quality interpolations.
Specifies the damping used for the Cholesky solver. This is normally not needed unless the solver is failing. In that case, start with a very small damping value like 0.00001 for example. Then use successively larger values like 0.0001, 0.001, 0.01, etc. until the solver succeeds.
Specifies the maximum number of iterations that the SVD solver performs. If the SVD solver fails, then increase this value until the solver succeeds.
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.
This is a simple example of using the BlendPose CHOP to deform some geometry using random tracker point positions.
The following examples include this node.