Rational ruled surfaces and their offsets

In this paper, geometric design problems for rational ruled surfaces are studied. We investigate a line geometric control structure and its connection to the standard tensor product B-spline representation, the use of the Klein model of line space, and algorithms for geometry processing. The main part of the paper is devoted to both classical and ''circular'' offsets of rational ruled surfaces. These surfaces arise in NC milling. Excluding developable surfaces and, for circular offsets, certain conoidal ruled surfaces, we show that both offset types of rational ruled surfaces are rational. In particular, we describe simple tool paths which are rational quartics. (C) 1996 Academic Press, Inc.