Vector channel node

Performs vector operations on a set or sets of channels.

See also: Blend, Object, Math, Switch

Vector math has several useful operations for use with channels, such as projections, dot products and distance/length calculations. This can be used for determining whether objects are facing each other, how far they are apart, or the angle between them.

This CHOP separates input channels into vectors based on the Vector Mask parameter, and applies a vector operation to each set individually. Two inputs can be used for binary vector operations. If the second input does not have as many vectors as the first, Vector cycles through the second input’s vectors.

Note	Channels that are not assigned to a vector mask will not be processed or present in the output.

Some vector operations produce a scalar result. In this case, the vector channels are removed and replaced with a single channel, whose name depends on the operation performed (such as 'dist', 'dot' or 'angle').

Additionally, an optional test can be done, comparing the vector operation results to a constant value or other vector channels. The result of this test can be used to remove vector channels or to produce zero/one channels representing where these vectors fail or pass the test. The Test tab contains the parameters for the vector test.

Parameters

Vector

Operation

Specifies which vector operation to perform on the vectors.

Magnitude of A	Computes the magnitude of A and replaces the vector channels with a single scalar channel, 'len'. If more than one vector is processed, the wildcard replacement is appended to 'len' (ie, (tx3,ty3,tz3) would produce len3). Only one input is required for this operation; the second input is ignored.
Normalize A	Reduces the vector to a unit-length vector. Only one input is required for this operation; the second input is ignored.
Distance between A and B	Computes the straight-line distance between A and B, as if they were points. This replaces the vector channels with a single channel named 'dist'.
A dot B	Computes the dot product of a vector from input 1 (A) with a vector from input 2 (B). If more vectors exist in A than B, the B vectors cycle back to the first vector. This replaces the vector channels with a single channel named 'dot'.
Normalized A dot B	Computes the dot product of A and B, but normalizes A and B first. This replaces the vector channels with a single channel named 'dot'.
Angle between A and B	Computes the angle between the two vectors, A and B, in degrees. This replaces the vector channels with a single channel named 'angle'.
A cross B	Computes the cross product of A and B. Both vectors must have exactly three components. The cross product is the vector that is orthogonal to both A and B.
Scalar Project B onto A	The scalar projection of B onto A determines the length of the vector produced when B is projected onto A. This replaces the vector channels with a single channel named 'proj'.
Vector Project B onto A	Projects the vector B onto the vector A, so that the result is parallel to A, and the magnitude is proportional to the angle between A and B.
Add	Adds vector A to B.
Subtract	Subtracts vector A from B.
Reverse Subtract	Subtracts vector B from A.
No operation	Passes vector A through as-is. Generally only useful when used with Perform Vector Test to compare vectors.

Vector Mask

A set of patterns which describe the members of the vectors. A wildcard '*' can be used to match more than one vector. A single vector will contain one channel from each pattern with the same wildcard replacement (ie, tx* ty* tz* would process vectors like (tx1,ty1,tz1) and (txa,txb,txc).

Vector Mask B

An optional parameter which sets the vector mask for vectors in the second input (B vectors), in case they happen to represent a different vector quantity (such as N, P or V). If disabled, the Vector Mask is used.

Vector Mask C

The vector mask for the third comparison input, similar to the above two. If disabled, the Vector Mask is used.

Align

For two-input vector operations, this parameter specifies which frame range to use if the inputs' frame ranges differ, and how to sample the inputs.

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 input channel’s start and end to that range.
Shift to Minimum	Find the earliest start and shift all input 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 input channels so they all end at that index. Extend all channels to the length of the longest one.
Shift to First Interval	Shift all input channels to the start of the first channel and sample all inputs using the first input’s range.
Trim to First Interval	Trim all input channels to first channel’s range.
Stretch to First Interval	Stretch all input channels to the first channel’s range.
Trim to Smallest Interval	Trim all input 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.

Test

A comparison test can be run after the initial vector operation, which can remove vectors that fail the test or produce a channel containing the samples which passed or failed for each vector.

Perform Vector Test

Enables the vector test on the result of the vector operation, which compares the result to a constant value or another input.

Result Vector Test

Describes how the vector is compared, with one of the inequality operations listed.

Test Against

The vector result is compared to a constant (Vector Constant) or vector/scalar channels from one of the three inputs.

Vector Constant

This parameter is the constant when Test Against is set to Constant. It will either have all fields enabled (if the vector result is a vector quantity) or only the first field enabled (if the result is a scalar).

Test Result

The output of the vector test can be the original vectors, modified vectors, or an on/off channel containing the test results.

Keep Original Vector A	If the test passes, the original A Vector is kept in the output. If the test failed, the vector channels are removed. This is useful for eliminating points or directions that fail the test in order to thin out the number of channels for faster downstream cooking.
Keep Result Vector	If the test passes, the result of the vector operation is kept in the output. If the test failed, it is removed.
Pass/Fail Channel	A single channel is created called 'test' for each vector, with the suffix of the vector appended to it. This channel is 1 for samples where the test passed, and 0 for where it failed. This can be used for controlling a Blend or Switch CHOP.

Pass If

When determining whether to keep or discard a channel (when Test Result is Keep Original Vector or Keep Result Vector), the test may pass for some samples and fail for others. Since a channel can only be entirely removed or entirely kept, vector channels that pass on some samples and fail on others must be resolved.

All Samples Pass	All samples in the vector test must pass the test in order for the vector channels to be kept.
One Sample Passes	Only one sample needs to pass the vector test in order for the vector channels to be kept.
A Fraction of the Samples Pass	A specified fraction (from 0.0 to 1.0) of the samples must pass the test in order for the vector channels to be kept.

Pass Fraction

If Pass If is set to 'Fraction of the Samples Pass', this sets the fraction of samples which must pass in order for the test to be considered successful. Zero means none need to pass, while 1.0 means that all samples must pass.

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.

Usages in other examples

Example name	Example for