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This CHOP interprets the input channels as a position vector and creates a channel with a value of 1 where the positions are stationary. This is useful for creating channels that describe when a character’s feet are planted, which can be used for foot locking in a crowd simulation.
Specifies the source of the position data.
The input channels are interpreted as a position vector.
Uses the position of the Target Object relative to the Reference Object.
Uses the world space position of an agent’s bone.
The object that is being compared to the reference object when Source is Object.
Optional object that acts as the basis for the comparison when Source is Object.
Specifies a local space position in the Target Object when Source is Object, or in the Transform Name when Source is Agent.
Specifies the frame range of the clip when Source is Object.
The path to a SOP containing an agent primitive. If the geometry contains multiple agent primitives, the first primitive in the Group will be used.
Specifies a primitive group for the SOP geometry.
The name of an animation clip in the agent primitive’s definition.
The name of a transform in the agent primitive’s rig.
Specifies the method used to determine when the joint is planted.
The joint is considered planted when its speed is less than the Speed Threshold.
Distance from Terrain
The joint is considered planted when it is within Distance Threshold of the terrain. This can provide more robust behaviour than the Speed Threshold method (such as when analyzing the ankle joint if a character is standing on their toes), but requires terrain geometry.
The speed threshold to use when determining if the joint is nearly stationary.
Specifies the source of the terrain geometry when Method is Distance from Terrain. This can either be a path to SOP geometry or a manually-specified plane.
The SOP geometry used when Method is Distance from Terrain and Terrain Source is SOP.
The origin point of the plane used when Method is Distance from Terrain and Terrain Source is Plane.
The normal of the plane used when Method is Distance from Terrain and Terrain Source is Plane.
The maximum distance from the terrain where the joint is considered planted.
Specifies the name of the new channel.
Blend In Frames
Specifies the number of frames over which the channel value changes from 0 to 1 before the foot plant begins.
Blend Out Frames
Specifies the number of frames over which the channel value returns to 0 after the foot plant ends.
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.
The following examples include this node.
This example demonstrates using heightfields for terrain adaptation in the crowd solver, and for collisions against ragdolls in the Bullet solver.