The purpose of a feature element is to identify a feature of an object. For example, consider the X-29 plane of figure 6b; an element can be used to delineate the nose of the plane. In feature-based morphing, elements come in pairs, one element in the source volume , and its counterpart in the target volume . A pair of elements identifies corresponding features in the two volumes, i.e. features that should be transformed to one another during the morph. For instance, when morphing the dart of figure 6a to the X-29 plane, the tip of the dart should turn into the nose of the plane. In order to obtain good morphs, we need to specify a collection of element pairs which define the overall correspondence of the two objects. These element pairs interact like magnets shaping a pliable volume: while a single magnet can only move, turn, and stretch the volume, multiple magnets generate interacting fields, termed influence fields, which combine to shape the volume in complex ways. Sculpting with multiple magnets becomes easier if we have magnets of various kinds in our toolbox, each magnet generating a differently shaped influence field. The elements in our toolkit are points, line segments, rectangles, and boxes.
In the following presentation, we first describe individual elements, and discuss how they identify features. We then show how a pair of elements guarantees that corresponding features are transformed to one another during the morph. Finally, we discuss how multiple element pairs interact.