Growing and Animating Polygonal Models of Animals

While there existmany computermodels of animal bodies, as polygonalmeshes and parametric surfaces, these are difficult to modify to take growth into account, or to animate. Growth data available fromthe literature usually is expressed as very sparse measurements over the body at various ages of the animal. We present here basic techniques to transfer growth data to computer models (especially polygonal meshes), which allows animation of the growth as well as animation of the body in the traditional sense. The main technique consists of defining local coordinate systems around the growing parts of the body, each one being transformed according to the relevant growth data while maintaining their relationship with the adjoining parts and the continuity of the surface. The local coordinates also permit ordinary animation mainly as relative rotation such as in articulated objects. We present examples with polygonal models of horses and cows, growth data from same, and motion fromMuybridge’s classic photographic data.