3.1.1 Polygonal and Polyhedral Models

In this and the next subsection, a solid representation of ${\cal O}$ will be developed in terms of a combination of primitives. Each primitive $H_i$ represents a subset of ${\cal W}$ that is easy to represent and manipulate in a computer. A complicated obstacle region will be represented by taking finite, Boolean combinations of primitives. Using set theory, this implies that ${\cal O}$ can also be defined in terms of a finite number of unions, intersections, and set differences of primitives.