Canonical ordering for graphs on the cylinder, with applications to periodic straight-line drawings on the flat cylinder and torus

TL;DR

This paper extends canonical ordering techniques to cylindric and toroidal graphs, enabling efficient, crossing-free, straight-line, periodic drawings on regular grids with provable size bounds.

Contribution

It introduces a canonical ordering for cylindric and toroidal graphs, allowing linear-time algorithms for periodic straight-line drawings with size guarantees.

Findings

Linear-time algorithms for periodic drawings of cylindric graphs.

Crossing-free, internally convex drawings on regular grids.

Grid size bounds proportional to number of vertices and face-distance.

Abstract

We extend the notion of canonical ordering (initially developed for planar triangulations and 3-connected planar maps) to cylindric (essentially simple) triangulations and more generally to cylindric (essentially internally) $3$-connected maps. This allows us to extend the incremental straight-line drawing algorithm of de Fraysseix, Pach and Pollack (in the triangulated case) and of Kant (in the $3$-connected case) to this setting. Precisely, for any cylindric essentially internally $3$-connected map $G$ with $n$ vertices, we can obtain in linear time a periodic (in $x$) straight-line drawing of $G$ that is crossing-free and internally (weakly) convex, on a regular grid $\mathbb{Z}/w\mathbb{Z}\times[0..h]$, with $w\leq 2n$ and $h\leq n(2d+1)$, where $d$ is the face-distance between the two boundaries. This also yields an efficient periodic drawing algorithm for graphs on the torus. Precisely, for any essentially $3$-connected map $G$ on the torus (i.e., $3$-connected in the periodic representation) with $n$ vertices, we can compute in linear time a periodic straight-line drawing of $G$ that is crossing-free and (weakly) convex, on a periodic regular grid $\mathbb{Z}/w\mathbb{Z}\times\mathbb{Z}/h\mathbb{Z}$, with $w\leq 2n$ and $h\leq 1+2n(c+1)$, where $c$ is the face-width of $G$. Since $c\leq\sqrt{2n}$, the grid area is $O(n^{5/2})$.