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## Describing 2D Shape with Axially Specified Subparts and Features

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