Capture Region SOP

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The Capture Region SOP defines capture region (cregion), which is a type of primitive which can be thought of as a modified tube primitive (a tube with half a sphere on either end). The hemispheres on the ends of the tubes are called "caps". Like any other primitive, each Capture Region has a primitive number and can be assigned primitive attributes. A Capture Region is simply a volume which is used to define the point capture weighting for a geometry. It is then animated to deform the geometry.

Capture Regions are always shown in wireframe (even in shaded mode) so that you can focus on the geometry for which the region will act on.


Parameters - Region Page

There are parameters to control the size, shape and position of the capture region. There are separate controls for the top and bottom half of the region. This allows you to edit one side of the bone at a time as you work through your character.

The Max/Min Weight parameter is used in the weighting of points. The closer a point is to the edge of the region, the smaller it's weight will be. By default the weight is 1 along the center axis of a region (more on this later), and 0 at the edge of the region. You can modify these weight extremities by through this parameter.

Orientation orient - - Defines the direction axis of the region. Use Z axis when the region is inside a bone object.


  • X Axis x -
  • Y Axis y -
  • Z Axis z -

Center t - - Position of the center of the region.

  • X tx -
  • Y ty -
  • Z tz -

Top Height theight - Height of the region from the centre to the top cap.

Top Cap tcap - - The X, Y, Z radii of the top/bottom hemisphere.

  • X tcapx -
  • Y tcapy -
  • Z tcapz -

Bottom Height bheight - Height of the region from the centre to the top cap.

Bottom Cap bcap - - The X, Y, Z radii of the top/bottom hemisphere.

  • X bcapx -
  • Y bcapy -
  • Z bcapz -

Max/Min Weight weight - - Defines the weight of a point exactly on the centre line and edge of the region respectively. Point weights in-between are blended.

  • weight1 -
  • weight2 -

Parameters - Display Page

Display Color color - - The Capture Region SOP<uses region colors for helpful feedback.

By default the region inherits the color of its containing object (via an expression).

  • Red colorr -
  • Green colorg -
  • Blue colorb -

How Weighting is Calculated

Weighting is based on distance to the center line of the region. The center line's length is the height of the tube and runs down its center. When viewed in cross-section, the distance is measured perpendicular to the center line for the tube section and radially for the hemisphere region. This scheme is shown below. The lines represent the distance of points along the edge of the region.

This weighting scheme gives continuous deformations to NURBS surfaces when the end cap section of one region is sized so that it touches the middle section of the next region, as shown below.


Capture regions shown with their containing bone objects.


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