On some union and intersection problems for polygons with fixed orientations

Abstract

Objects with fixed orientations play an important role in many application areas, for instance VLSI design. Problems involving only rectilinearly oriented (rectangular) objects, as a simplest case, have been studied with the VLSI design application in mind. These objects can be transistors, cells or macros. In reality, they are more suitably represented by polygons rather than just rectangles. In this note we describe how to perform a general decomposition of a set of polygons with fixed orientations in order to solve various computational geometry problems which are important in VLSI design. The decomposition is very simple and efficiently computable, and it allows the subsequent application of algorithms for the rectilinear case, leading to some very efficient and some optimal solutions. We illustrate the technique in detail at the problem of finding the connected components of a set of polygons, for which we derive an optimal solution. The wide applicability of the method is then demonstrated at the problem of finding all pairs of intersecting polygons, yielding an optimal solution. © 1986 Springer-Verlag.