| On this page |
The most common use for this CHOP is to extract translation and rotation channels from DOP objects to apply to Geometry Objects. But you can also use it to extract collision information, velocity values, constraint information, and so on.
You can use wild cards when choosing the information to extract, so it is very easy to extract large volumes of information from a simulation.
Note
The Units must be set to Seconds if you want to pick up anything from DOPs before frame 24, since the CHOP starts at index 1 (which is 1 second in DOP time).
Parameters ¶
Dynamics ¶
DOP Path
The path to the DOP data to extract the information from.
This consists of a DOP Network path, an object
specification, and a data name. The format of the string is:
dopnet:objectspec/datapath, just as in the dopfield
expression. The objectspec can contain wildcards to match
a number of objects, but the dopnet and datapath
components do not support wildcards. If just a DOP Network
path is specified in this parameter, such as /obj/dopnet1,
then it is assumed that the Position information from all
objects in that DOP Network should be extracted. An
equivalent value for this parameter would be
/obj/dopnet1:*/Position.
Record Name
This parameter controls which record within the simulation data is to be examined. The most common value is Options which is where most simulation data stores its attributes. In the case of impact information, this field would be Impacts.
Record Numbers
This numerical pattern specifies the record numbers from
which this CHOP should extract its information. The Options
record generally has only one record. But when extracting
impact information, a value of "*" can be used to extract
all impact records. A range can also be specified. "0-4"
can be used to extract the first five impact records.
Field Names
Controls which fields are extracted from the chosen records
in the simulation data. This field accepts wild cards. To
extract just the translations and rotations from Position
data, for example, set this parameter to "t? r?". To
extract all available fields, use the default value of
"*".
Include Record Number In Track Name
If multiple records are being extracted from the simulation data, you should turn on this option to ensure the channel names created for each record are unique. Otherwise, the values from each record will overwrite the values from the previous record. This parameter defaults to being off because when extracting only a single record the numerical suffix is generally not useful.
Method
Controls the way data is extracted from the DOP Network.
Dynamic
The CHOP extracts only the data from the current timestep. Whenever the DOP Network changes to a new timestep, the values in this CHOP are updated.
Cached
The CHOP cooks the DOP Network for the whole duration of the CHOPs time range. All data is extracted and preserved. Changes to the DOP Network do not cause this CHOP to recook, as that could be very time consuming. To update Cached values in this CHOP, use the Update button.
Update
Forces this CHOP to resimulate the DOP Network and recache all values if the Method parameter is set to Cached. Pressing this button is the only way to update the Cached values.
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 start time of the channels.
Sample Rate
The sample rate of the channels.
Extend Left
The left extend conditions.
Extend Right
The right extend conditions.
Default Value
The default value for extend conditions.
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 ¶
DynamicLights Example for Dynamics channel node
This example demonstrates how to use the Dynamics CHOP to extract impact data from a DOPs simulation, and then modify the data to control lights in the scene.
ExtractTransforms Example for Dynamics channel node
This example demonstrates the use of the Dynamics CHOP to pull transformation information out of a DOP simulation and apply it to Objects.
