Houdini 19.0 Nodes Channel nodes Constraint Points

Constraint Points channel node

Position and Orient an object using point positions from a geometry.

Since 16.0

The Constraint Points CHOP computes a position from a group of points on a geometry. It can also optionally compute a rotation to make the object look at direction.

Parameters

Constraint Points

SOP Path

The surface geometry to fetch the points from.

Mode

Groups can hold points or primitives. When using primitives, the points indices are extracted and the constraint works on the points.

Group

The point or primitive group (or numbers) based on which the local surface frame is built. The group centroid is set as the frame origin.

Weights

The weights assigned to the first three points in the group.

This parameter allows you to fine tune the exact position of the rivet origin on the plane constructed from the first three points. For example, the weights (0.5, 0.5, 0) will place the origin half way between the first and the second point. NOTE

The weights should not add up to 0. The points beyond the third one, if any, are assigned weight values of 1.

Look At Mode

Defines how to compute the Look At direction. The Lookat position can be overriden by connecting the second input.

None

Disable the Look At and keep the existing orientation.

Direction Attribute from Points

Use the average of the Direction Attribute from points in the group.

Direction Vector from P0 to P1

Use the first and second points to define a vector.

Normal Vector from P0,P1,P2 Plane

Use the normal vector of the plane made of the first 3 points.

Look Up Mode

Defines how to compute the Look At Up vector. The Look Up vector can be overriden by connecting the third input.

Up Vector

Use the Up Vector from the parameter pane.

Up Vector Attribute from Points

Use the average of the Up Attribute from points in the group.

Direction Vector from P0 to P1

Use the first and second points to define a vector.

Normal Vector from P0,P1,P2 Plane

Use the normal vector of the plane made of the first 3 points.

Direction Attribute

The attribute name representing the direction vector on the geometry.

Up Attribute

The attribute name representing the Up Vector on the geometry.

Look At Axis

Defines which of the 6 axis ( X-, Y-, Z-, X+, Y+, Z+) is oriented along the path.

Look Up Axis

Defines which of the 4 allowed axis act as the up direction. The allowed axis changes based on the Look At Axis. You can’t use the same axis to define the look at and up directions.

Roll

Rotation around the direction vector in degrees.

Channel

Align

The alignment option to use.

Extend to Min/Max

Find the earliest start and latest end, and extend all inputs to that range using the extend conditions.

Stretch to Min/Max

Find the earliest start and latest end, and stretch every channel’s start and end to that range.

Shift to Minimum

Find the earliest start and shift all channels so they all start at that index. All channels are extended to the length of the longest one.

Shift to Maximum

Find the latest end and shift all channels so they all end at that index. Extend all channels to the length of the longest one.

Shift to First Interval

Shift all channels to the start of the first channel and sample all inputs using the first input’s range.

Trim to First Interval

Trim all channels to first channel’s range.

Stretch to First Interval

Stretch all channels to the first channel’s range.

Trim to Smallest Interval

Trim all channels to the smallest start/end interval. The start and end values may not come from the same channel.

Stretch to Smallest Interval

Stretch all channels to the smallest start/end interval. The start and end values may not come from the same channel.

Range

Specifies the range of data to generate.

Use Full Animation Range

All of the animated range.

Use Current Frame

Only the sample at the current frame.

Use Start/End

The range is specified from the Start and End parameters.

Use Value Animation

The range is taken from range of keys available in the evaluated Value parameters.

Start

The start time of the channel range.

End

The end time of the channel range.

Sample Rate

The sample rate of the CHOP.

Number of Threads

The number of separate threads to use to evaluate the channel samples. The default is no threading.

Since Houdini evaluates the VEX program for each sample in the input geometry, it can benefit greatly from threading on a multi-processor or multi-core machine when the CHOP nodes have many samples.

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.

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.

See also

Constraint Points