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This CHOP adds, removes or updates attributes of the input chop. Currently there is only one attribute type, a "quaternion". This attribute type is used to group rotation channel triplets (rx,ry,rz) together.
Rotations sometimes need to be grouped together since interpolations on independent X, Y and Z rotations do not produce smooth results. Rotations often need Quaternion interpolation to rotate through the most direct path.
Operations such as resampling and blending recognize the rotation triplet with the "quaternion" attribute. They blend or resample the rotation channels using "spherical linear interpolation". Ordinary interpolation can produce poor blending results, whereas quaternion blending produces the shortest rotation path between two sets of rotations.
See some of the chops that use the attribute: the 
Sequence
CHOP and 
Composite CHOP.
Other chops may quietly use
the Quaternion attribute, such as the Object, Stretch and Resample
chops.
The Scope is needed to specify the channels that will be grouped.
Standard Options and Local Variables
Scope
Selects which channels are X,Y and Z rotations. The channels can be typed in explicitly, or using wildcards. If the number of X,Y and Z rotations selected do not match, an error will occur. Example:
*r[xyz]
Parameters
Quaternion
Function
The function to perform on the attributes:
Pass Through
Leaves the attributes untouched.
Replace
Erases previous attributes and replaces them with the new ones.
Append
Keeps previous attributes and combines them with the new attributes. If an attribute already exists on a channel and append attempts to overwrite it, an error will occur.
Remove
Removes all scoped channels' attributes.
Rotate Order
Sets the rotation order of the rotation triplet.
Scope
Selects which channels are X,Y and Z rotations. The channels
can be typed in explicitly, or using wildcards. If the
number of X,Y and Z rotations selected do not match, an
error will occur. For example: *r[xyz].
Common
Some of these parameters may not be available 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.
