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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.
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).
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
objectspec can contain wildcards to match
a number of objects, but the
components do not support wildcards. If just a DOP Network
path is specified in this parameter, such as
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
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.
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.
can be used to extract the first five impact records.
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.
Controls the way data is extracted from the DOP Network.
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.
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.
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.
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.
Specify the range using the Start/End parameters.
The start time of the channels.
The sample rate of the channels.
The left extend conditions.
The right extend conditions.
The default value for extend conditions.
Some of these parameters may not be available on all CHOP nodes.
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:
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 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.
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).
When you change the Units parameter, the existing parameters are not converted to the new units.
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.
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 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.
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.