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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.
Tips
-
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.
Parameters
Kinematics
Solver Type
Specifies the solver to use to generate the channels.
Inverse Kinematics
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.
Chain Names
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
are found.
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 xOrd and rOrd channels are
integers corresponding to index of the regular transform/rotation
order parameter menus.
Bone-specific
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
are: begin[xyz]range end[xyz]range [xyz]damp [xyz]rolloff.
Pre-transform Name
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: t[xyz].
Twist Affector
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: t[xyz].
IK Twist
For the Inverse Kinematics solver, this parameter specifies an additional twist angle to be applied to the solution bone angles.
IK Dampening
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.
Blend
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 1,
it produces the solved bone rotation values. If the Blend input
is provided, then the channel value there will be used for blending instead.
Straighten Solutions
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.
Clean Rotations
Modifies output rotation values such that they contain values as close as possible to the rest angle rotations without changing the solution.
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
SimpleIKSolver Example for IKSolver channel node
This example demonstrates how to use the IKSolver CHOP.
The following examples include this node.
SimpleIKSolver Example for IKSolver channel node
| See also |
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