Dynamics channel node

Extracts any information from a DOP simulation that is accessible through the dopfield expression function.

All Parameters Example files

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.

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.

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.

Example files

ExtractTransforms

$HFS/houdini/help/examples/nodes/chop/dynamics/ExtractTransforms.cmd

Load | Launch

This example demonstrates the use of the Dynamics CHOP to pull transformation information out of a DOP simulation and apply it to Objects.

Usages in other examples

Example name Example for
Lookup

Lookup channel node

Load | Launch