Matching Models and Anatomy

Continuing advances in digital modeling and computer-aided design have produced a wealth of convincing models. Models ranging from household objects to animals can be purchased over the Internet, or easily generated using digitizers or sophisticated modeling software. However, models representing non-rigid, articulated creatures such as humans and animals rarely come with the articulation information essential for their realistic animation. When an existing surface model is available, an underlying articulated skeleton must be associated with it so that, when the joints move during animation, the surface model moves in an appropriate fashion. We are developing methods that make this process easier and faster. Much of this work was done by Jeffrey Lapierre.

Super Segments

Super segments are simple kinematic subchains of the hierarchy. Joints within a super segment can be controlled as a unit, using rotations, translations and scalings, and inverse kinematics. The left image shows the basic horse hierarchy and the right image shows initial super segments of this hierarchy. The user can add and delete super segments.

Distributed Rotations

Interactively dragging the axis of a super segment distributes a rotation to the joints within it. By default the distribution is equally weighted to each joint.

The user can weight the distribution by interactively altering a weighting function in the super segment window.

Distributed Translations

Interactively dragging the node of a super segment distributes a longitudinal transation to the joints within it. By default the distribution is equally weighted to each joint. It can be weighted as described above for rotations.

Inverse Kinematics

The super segment can also be made to follow a worldspace position using inverse kinematics.

Matching a Brachiosaurus to a Horse Skeleton

We show a horse hierarchy matched to a brachiosaurus skin from Viewpoint DataLabs. At left we show the horse skeleton in its initial configuration by the dinosaur. In the center, we show the hierarchy after matching. At right, we show the skin with underlying components.

The Brachiosaurus in New Positions

After matching, the skin vertices are attached to their nearest underlying components. The skin follows the underlying components during animation, and elastically adjusts itself.