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The axial specification method provides the following basic shape description
mechanisms:
- Shape is described in terms of a combination of distinct convex sub
parts, and two dimensional shape features.
- Relative size is described in terms of the lengths of object axes,
subpart axes and feature axes.
- The position of subparts and features within an object is described
with respect to the object axes, subpart axes and feature axes.
- Relative position of separate objects is described in terms of contact
between features or subparts, and relative orientation of object axes.
The most prominent aspect of this two dimensional shape representation method
is the use of axes to describe both size and orientation, and that every
element of the shape description has axes associated with it. The axes
associated with important shape description levels are as follows:
- Overall Shape:
- The major and minor axes. These were described above as
the widest and narrowest extents respectively of the shape.
More
precisely, the major axis is the longest perpendicular line that can be
drawn between two parallel tangents to the shape boundary, and the
minor axis is the shortest such line. ``Tangents'' may span vertices,
so that the height of a triangle, for instance, could become an axis
by this definition.
- Convex Subparts or ``Imples'':
- The major and minor axes, and the waist.
Major and minor axes of imples are defined as for overall shape, with the waist
being considered part of the imple boundary during axis construction.
- Vertices:
- The angle bisector.
- Edges:
- The chord between edge extremities, and the normal to this
chord.
Next: Primitive Shape
Up: Qualitative Two Dimensional Shape
Previous: Qualitative Two Dimensional Shape
Alan Blackwell
2000-11-17