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.