Authors
IC Braid, RC Hillyard, IA Stroud
Publication date
1980
Volume
123
Publisher
Academic press
Description
In computer-aided design of three-dimensional solid objects, the volumetric approach in which simple solids such as cubes and cylinders are added or subtracted to make new shapes, offers many advantages and has received much attention in recent years. It has, at least from the theoretical point of view, the merit that only true solids can be designed [Requicha 1977]. This property contrasts with draughting systems where, because the shape is described in lower-level terms such as lines and points, objects can be created in the computer that have no physical equivalent. For example it may be quite possible to design a Klein bottle or a shape with dangling edges or faces.
However, design of certain kinds of shape, particularly those known as 2D shapes, is awkward in a pure volume-based system. Thus the original BUILD program [Braid 1973] incorporated a variable primitive made by constructing a right prism on a base bounded by straight lines and circular arcs. The designer specified the boundary in a simple language using methods closer to traditional draughting practice. He could round off sharp corners or draw a line tangent to a circle. Although from a designer's point of view the input was more natural, the assurance that only solids could be built was lost. For example, one could build a right prism on a figure-of-eight base; not until a later volumetric operation failed would one discover that an improper shape had been constructed.
Total citations
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