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This filter CHOP generates inverse kinematics rotations for bone chains similar to the InverseKin CHOP. The primary difference is that the input specification is taken entirely from input channels instead of object paths.
The format of the input channel names are expected to follow the
object_name:parameter_name format where _object_name_ is specified by the new
Name parameters described below and _parameter_name_ is the name of the
parameter that the InverseKin CHOP normally fetches from the object scene. If a
particular channel is missing from its input, then the default object parameter
values will be used instead.
There are three inputs.
The goal and twist affector positions must be relative to the parent space of the first bone. You can do this by enabling Use Reference Bone Length on the Object CHOP.
If the bone objects you are transforming have a pretransform, then these transforms should be included in the second input. The Object CHOP can be used to easily produce transforms for the second input.
For speed, it is useful to set the second input to only produce channel values at frame 1, since the rest bone chain values are not typically animated.
Specifies the solver to use to generate the channels.
Uses IK solver. The solution is uniquely defined by the end affector position. Constraint parameters are ignored.
IK With Constraints
Uses a modified IK solver. The solution depends on the previous solution. Constraint parameters are used to limit the range of motion.
Specifies the _object_name_'s to be used for channels in the Rest
input. The order of the names will be interpreted as the hierarchy
of the object chain. If the value is
*, then the chain names
will be taken from the second input, in the order in which they
The transform parameter names that are accepted by the Inverse Kinematics
Solver Type are:
xOrd rOrd t[xyz] r[xyz] s[xyz] scale p[xyz].
Note that the channel values of
rOrd channels are
integers corresponding to index of the regular transform/rotation
order parameter menus.
parameter names accepted are:
R[xyz] length ikdamp.
If an _object_name_ has none of the bone-specific channels, then it will be treated as non-bone (ie. the length of the previous bone will not be used).
Additional parameter names used by the IK with Constraints Solver Type
begin[xyz]range end[xyz]range [xyz]damp [xyz]rolloff.
Specifies the token used for pre-transforms of the Chain Names. The full channel name used for the second input will be the chain name, pre-transform name, and parameter name all concatenated together in this order.
End Affector Name
Specifies the _object_name_ to be used for the end affector position channels. The end affector is used as goal for the bone chain.
The parameter names accepted from the Source input are:
For the Inverse Kinematics solver, this specifies the _object_name_ used for twist affector position channels. The twist affector controls the twist orientation of the solution bone angles.
The parameter names accepted from the Source input are:
For the Inverse Kinematics solver, this parameter specifies an additional twist angle to be applied to the solution bone angles.
For the Inverse Kinematics solver, this parameter represents how easily the end bone can be pulled off the end affector as the bone chain is stretched out.
This option blends between the local bone rotation values (found
in the Source input) and the solved solution. When this value is
0 it produces the local bone rotation values and when it is
it produces the solved bone rotation values. If the Blend input
is provided, then the channel value there will be used for blending instead.
When this checkbox is turned on, the bone chain will completely straighten out in the direction of the goal if the IK goal is farther away than the length of the bone chain (with a tolerance of the tracking threshold). If this checkbox is turned off, no attempt is made to further straighten the IK solution. By default it is turned off because it is faster.
Tracking Threshold Factor
This value specifies the accuracy threshold for Inverse Kinematic solutions. Use smaller values for more accurate solutions at the expense of more computation time. Use larger values to save computation time at the expense of getting less accurate solutions.
Modifies output rotation values such that they contain values as close as possible to the rest angle rotations without changing the solution.
Some of these parameters may not be available on all CHOP nodes.
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:
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 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.
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).
When you change the Units parameter, the existing parameters are not converted to the new units.
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.
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 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.