Bounding Model

Once you have created a skeleton, you can select a joint or object in the hierarchy and create a bounding model around your selection.

As the name suggests, a bounding model describes the area of influence around the joint, either by limiting the assignment of envelope vertices, or forcing certain vertices to be assigned to a specific skeleton model. Bounding models are only useful for skeletons with envelopes, but can be created before assigning the envelope and edited as required.

Bounding models are retained even if the envelope is cut from the skeleton and another is assigned.

Bounding models are displayed only when Show->Controls is activated. As the "children" of the associated joints, they use the same display colour.

You can scale, rotate, and/or translate them as desired.

Notes

Bounding models are applied only during initial assignment and automatic reassignment.

If you create/edit a bounding model after you have already assigned an envelope, you must choose Skin->Reassign Automatically to implement the associated changes in assignment.

Procedure

1. Draw one or more chains and/or models. Place them in a hierarchy as desired.
2. Define this as a skeleton. You can either:

• Choose Skeleton->Group as Skeleton and click the left mouse button to Set Skeleton.
  or
• Assign an envelope to the hierarchy.

In either case, the hierarchy is now defined as a skeleton.

3. If you want to verify vertices' assignment, choose either Skin->Modify Weights to view weighting values in the Envelope Weights dialogue box.
4. If you want to create a bounding model to control vertices' assignment, select a skeleton element and choose Skin->Envelope Assignment->Bounding Model->Inclusive/Inclusive Limit/Exclusive.
5. Select the shape of the bounding model using the mouse buttons.

• Left mouse button creates a bounding box.
• Middle mouse button creates a bounding cylinder.
• Right mouse button creates a bounding sphere.

6. You can then scale, rotate, and translate the bounding model.
   
   Note:
   
   You can also edit the geometry of a bounding box.
   
   
7. If you assigned an envelope before creating or editing the bounding model, choose Skin->Reassign Automatically to implement the changes in assignment.

Types

Bounding models can be combined for more realistic deformation. For example, to achieve a progressively diminishing influence of the joint, you could use both an Inclusive bounding and an Inclusive Limit box. For details on how this works, see Combining Bounding Models of the Modelling User's Guide.

Inclusive Limit

This type of bounding model defines the joint's zone of influence, similar to a clipping operation. When using Inclusive Limit:

• Any vertex falling outside its boundary cannot be assigned to the joint.
• Skeleton elements outside the bounding model can still affect the vertices inside the bounding model.

Inclusive

Any vertex falling within the bounding model is assigned 100% to the associated skeleton element, without regard to relative proximity to the skeleton element.

Points falling outside any inclusive bounding model are assigned and weighted (according to their relative proximity) to the n closest joints; n is defined in Default nb of joints assigned in the Envelope Initial Assignment dialogue box. The default is 2.

Exclusive

Any vertex falling within the bounding model is prevented from being assigned to the associated joint.

Shapes

All types of bounding model come in the same three shapes: a box, a cylinder or a sphere. Only the box shapes can be edited. You can tag and transform their points to define a more accurate area over the envelope.

Last updated 02-apr-1998