A Faster Algorithm for Computing Straight Skeletons

Abstract

We present a new algorithm for computing the straight skeleton of a polygon. For a polygon with $n$ vertices, among which $r$ are reflex vertices, we give a deterministic algorithm that reduces the straight skeleton computation to a motorcycle graph computation in $O(n (\log n)\log r)$ time. It improves on the previously best known algorithm for this reduction, which is randomized, and runs in expected $O(n \sqrt{h+1}\log^2 n)$ time for a polygon with $h$ holes. Using known motorcycle graph algorithms, our result yields improved time bounds for computing straight skeletons. In particular, we can compute the straight skeleton of a non-degenerate polygon in $O(n (\log n) \log r + r^{4/3+\varepsilon})$ time for any $\varepsilon>0$. On degenerate input, our time bound increases to $O(n (\log n) \log r + r^{17/11+\varepsilon})$.