Transversal structures on triangulations: A combinatorial study and straight-line drawings

This article focuses on a combinatorial structure specific to triangulated plane graphs with quadrangular outer face and no separating triangle, which are called irreducible triangulations. The structure has been introduced by Xin He under the name of regular edge-labelling and consists of two bipolar orientations that are transversal. For this reason, the terminology used here is that of transversal structures. The main results obtained in the article are a bijection between irreducible triangulations and ternary trees, and a straight-line drawing algorithm for irreducible triangulations. For a random irreducible triangulation with nn vertices, the grid size of the drawing is asymptotically with high probability 11n/27×11n/2711n/27×11n/27 up to an additive error of O(n). In contrast, the best previously known algorithm for these triangulations only guarantees a grid size (⌈n/2⌉−1)×⌊n/2⌋(⌈n/2⌉−1)×⌊n/2⌋.