Convexity Algorithms in Parallel Coordinates

Abstract

With a system of parallel coordinates, objects in RN can be represented with planar “graphs” (i.e., planar diagrams) for arbitrary N [21]. In R2, embedded in the projective plane, parallel coordinates induce a point ← → line duality. This yields a new duality between bounded and unbounded convex sets and hstars (a generalization of hyperbolas), as well as a duality between convex union (convex merge) and intersection. From these results, algorithms for constructing the intersection and convex merge of convex polygons in O(n) time and the convex hull on the plane in O(log n) for real-time and O(n log n) worst-case construction, where n is the total number of points, are derived. By virtue of the duality, these algorithms also apply to polygons whose edges are a certain class of convex curves. These planar constructions are studied prior to exploring generalizations to N-dimensions. The needed results on parallel coordinates are given first. © 1987, ACM. All rights reserved.