On Self-Approaching and Increasing-Chord Drawings of 3-Connected Planar Graphs

TL;DR

This paper investigates self-approaching and increasing-chord graph drawings, demonstrating their existence in certain classes of planar graphs and trees, and establishing complexity and non-existence results in Euclidean and hyperbolic geometries.

Contribution

It proves that triangulations admit increasing-chord drawings in the Euclidean plane, shows exponential resolution requirements for certain trees, and characterizes trees with such drawings.

Findings

Triangulations admit increasing-chord drawings in the Euclidean plane.

Strongly monotone drawings of trees require exponential resolution.

Some binary cactuses do not admit self-approaching drawings.

Abstract

An $st$-path in a drawing of a graph is self-approaching if during the traversal of the corresponding curve from $s$ to any point $t'$ on the curve the distance to $t'$ is non-increasing. A path has increasing chords if it is self-approaching in both directions. A drawing is self-approaching (increasing-chord) if any pair of vertices is connected by a self-approaching (increasing-chord) path. We study self-approaching and increasing-chord drawings of triangulations and 3-connected planar graphs. We show that in the Euclidean plane, triangulations admit increasing-chord drawings, and for planar 3-trees we can ensure planarity. We prove that strongly monotone (and thus increasing-chord) drawings of trees and binary cactuses require exponential resolution in the worst case, answering an open question by Kindermann et al. [GD'14]. Moreover, we provide a binary cactus that does not admit a self-approaching drawing. Finally, we show that 3-connected planar graphs admit increasing-chord drawings in the hyperbolic plane and characterize the trees that admit such drawings.