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The Geometry CHOP uses a geometry object to choose a SOP from which the channels will be created. The channels are created from the point attributes of a SOP, such as the X, Y and Z of the point position.
The SOP can select a subset of the points using Point Groups. The set of attributes that are converted to channels are chosen using the names of the attributes seen on the Info pop-up of SOP tiles.
See the Channel SOP ¶
Note
This CHOP works in tandem with the Geometry > Channel SOP. Point data can be modified in CHOPs and then fed back to SOPs through the Channel SOP, therefore be sure to take a look at the Channel SOP description.
Parameters ¶
Geometry ¶
SOP
Retrieves the geometry from the SOP pointed to by this path.
Group
Fetch only the points within this point group. If blank, all points are fetched.
Method
The geometry fetch method.
Static
Creates one channel for each attribute, and all points use this channel (the first point resides at index 0, the next at 1, and so on). The length of the channels will be the number of points fetched.
Animated
Creates one channel per attribute per point. The channels show the animation of each point’s position/attribute values.
Attribute Scope
A string list of attributes to fetch from the SOP. The common attributes are:
P
Point position (X, Y, Z) - 3 values.
Pw
Point weight with a value of 1.
Cd
Point color (red, green, blue) - 3 values.
Alpha
Point alpha with a value of 1.
N
Point normal value (X, Y, Z) - 3 values.
uv
point texture coordinates (U,V,W) - 3 values.
Matrix Attribute Scope
A string list of 3×3 or 4×4 matrix attributes to fetch from the SOP and then decompose into their translation, rotation, scale, and shear channels. If Output Shear Channels is disabled, then shear channels will not be created.
3×3 matrices are cracked into up to 9 channels: xyz channels for each of the matrices' rotation, scale, and shear components in that order.
4×4 matrices are cracked into up to 12 channels: xyz channels for each of the matrices' translation, rotation, scale, and shear components in that order.
Rotation Order
The order in which the extracted euler rotations can occur to recreate the matrices specified within Matrix Attrib Scope.
Output Shear Channels
If this option is selected, then the shear channels for the attributes specified within Matrix Attribute Scope will output.
Rename Scope
The names to use for the newly fetched attributes. There must be one name per attribute, so an attribute scope of P
should have a rename scope with three names (like tx ty tz).
Filter by Attribute
Specifies a point integer attribute to use as bitmask based of rename scope index.
If the rename scope is set to “tx ty tz”, the first 3 bits of the integer determines which channels are created.
-
tx bit is activated by a value of 1.
-
ty bit is activated by a value of 2.
-
tz bit is activated by a value of 4.
-
A value of 3 means the tx and ty bits are active.
-
A value of 5 means the tx and tz bits are active.
-
A value of 6 means the ty and tz bits are active.
-
A value of 7 means the tx,ty,tz bits are active.
Note
This only applies to Animated Method.
Transform Object
If a transform object is specified, the point values will be represented relative to that object’s origin and rotation.
Organize by Attribute
Rebuilds the fetched channels by the value of this attribute. A common example is the id
attribute found in particles. A channel is built for each unique id since the number of points may vary.
Note
This only applies to Animated Method.
Organize Method
How to handle missing channels when using Organize by Attribute.
Revert to First Value on Error
Use the first valid value of a channel when the id
attribute can’t be
found.
Hold Last Value on Error
Use the last valid value of a channel when the id
attribute can’t be
found.
Set to Error Value on Error
Use the Organize Error Value when the id
attribute can’t be found.
Set to Found Status
Set the channel value to 1 if the id
attribute is found or zero
otherwise.
Note
This only applies to Animated Method.
Organize Error Value
Use the Organize Error Value when the id
attribute can’t be found.
Note
This only applies when the Organize Method is Set to Error Value on Error.
Point Name Attribute
Specifies a point string attribute to use as a prefix when building channel names. Without this, channels are named by appending the point index. This makes it possible to use a single CHOP node to export point attributes to node parameters.
Note
This only applies to Animated Method.
Channel ¶
Channel Range
Indicates how much of the channel to cook.
Use Full Animation Range
All of the current global animation range.
Use Current Frame
Only the sample at the current frame.
Use Start/End
Specify the range using the Start/End parameters.
Start/End
The time range over which to fetch the geometry values when Animated Method is selected.
Sample Rate
The sample rate to use for the fetched channels.
Extend Left
The extend condition before the channel’s beginning.
Extend Right
The extend condition after the channel’s ending.
Default Value
The value of the default value extend condition.
Common ¶
Some of these parameters may not be available on all CHOP nodes.
Scope
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in 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.
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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the 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 of the time parameters.
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, the existing parameters are not converted to the new units.
Time Slice
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the 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 to it for display in the graph, but you can override the color with the 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 ¶
Geometry Example for Geometry channel node
This is an example of how the Geometry CHOP can fetch data from a SOP and turn that data into channels.
In this case, the Geometry CHOP pulls in the position of every point in a Superquad SOP and creates channels from that data.
GeometryMethods Example for Geometry channel node
This example demonstrates using the different methods of the Geometry CHOP - Animated and Static.
See also |