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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.
Parameters
Fit
Interpolant
Interpolation method.
Radial Basis Functions
This class of interpolants provide smooth results that will likely match the example data.
Hyperplane
This interpolant will create a plane of best fit. The results will likely not match the example data.
Clamp Input
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.
Kernel
This specifies the kernel function used for the Radial Basis Functions interpolant. Different kernel functions will result in varying fits.
Exponent
Specifies the exponent used for the Thin Plate kernal function. Larger values will give smoother results.
Fall Off
Specifies the fall off factor for the Gaussian, Multiquadric, Inverse Multiquadric, and Exponential Bump kernel functions. Larger values will give smoother results.
Solver
Specifies the solver method used for the interpolation.
Cholesky
The Cholesky solver is faster but not as stable.
SVD
The SVD solver is slower but will produce the higher quality interpolations.
Damping
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.
Maximum Iterations
Specifies the maximum number of iterations that the SVD solver performs. If the SVD solver fails, then increase this value until the solver succeeds.
Common
Some of these parameters may not be available 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.
Examples
BlendPoseBasic Example for BlendPose channel node
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.
BlendPoseBasic Example for BlendPose channel node
| See also |
Composite
