Triangulating a Polygon with Holes in Optimal (Deterministic) Time

TL;DR

This paper presents a new deterministic algorithm for triangulating polygons with holes in optimal linearithmic time, improving previous randomized and deterministic methods, and extends to computing trapezoidal decompositions with intersection constraints.

Contribution

The authors introduce an optimal deterministic $O(n + h\,log h)$-time algorithm for polygon triangulation with holes, surpassing prior methods and applicable to intersecting polygonal chains.

Findings

Achieves optimal $O(n + h\log h)$ triangulation time.

Extends to trapezoidal decomposition with limited intersections.

Uses Chazelle's linear-time polygon triangulation as a black box.

Abstract

We consider the problem of triangulating a polygon with $n$ vertices and $h$ holes, or relatedly the problem of computing the trapezoidal decomposition of a collection of $h$ disjoint simple polygonal chains with $n$ vertices total. Clarkson, Cole, and Tarjan (1992) and Seidel (1991) gave randomized algorithms running in $O(n\log^*n + h\log h)$ time, while Bar-Yehuda and Chazelle (1994) described deterministic algorithms running in $O(n+h\log^{1+\varepsilon}h)$ or $O((n+h\log h)\log\log h)$ time, for an arbitrarily small positive constant $\varepsilon$. No improvements have been reported since. We describe a new $O(n + h\log h)$-time algorithm, which is optimal and deterministic. More generally, when the given polygonal chains are not necessarily simple and may intersect each other, we show how to compute their trapezoidal decomposition (and in particular, compute all intersections) in optimal $O(n + h\log h)$ deterministic time when the number of intersections is at most $n^{1-\varepsilon}$. To obtain these results, Chazelle's linear-time algorithm for triangulating a simple polygon is used as a black box.