IKSolver channel node

Solves inverse kinematics rotations for bone chains.

All Parameters Example files

See also: InverseKin, Object, ObjectChain, Fetch

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.

First input

This contains the bone chain parameters that are typically animated. For example, the bone FK rotations and the goal object position.

Second input

This contains the bone chain parameters that are typically non-animated such as the bone rest angles.

Third input (optional)

This contains a single channel to be used for blending. If this input is omitted, then the Blend parameter value is used instead.

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 avaiable 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.

Example files

SimpleIKSolver

$HFS/houdini/help/examples/nodes/chop/iksolver/SimpleIKSolver.otl

Load | Launch

This example demonstrates how to use the IKSolver CHOP.

Usages in other examples

Example name Example for