Constrained Generalized Delaunay Graphs Are Plane Spanners

TL;DR

This paper demonstrates that constrained generalized Delaunay graphs based on any convex shape are plane t-spanners of the visibility graph, with specific bounds improved for rectangular shapes, enhancing understanding of geometric spanners.

Contribution

It establishes that constrained Delaunay graphs are plane t-spanners for any convex shape and provides improved bounds for rectangular shapes.

Findings

Constrained Delaunay graphs are plane t-spanners regardless of the convex shape.

The spanning ratio for rectangular shapes is bounded by rom the shape's dimensions.

The results hold for arbitrary convex shapes, generalizing previous work.

Abstract

We look at generalized Delaunay graphs in the constrained setting by introducing line segments which the edges of the graph are not allowed to cross. Given an arbitrary convex shape $C$, a constrained Delaunay graph is constructed by adding an edge between two vertices $p$ and $q$ if and only if there exists a homothet of $C$ with $p$ and $q$ on its boundary that does not contain any other vertices visible to $p$ and $q$. We show that, regardless of the convex shape $C$ used to construct the constrained Delaunay graph, there exists a constant $t$ (that depends on $C$) such that it is a plane $t$-spanner of the visibility graph. Furthermore, we reduce the upper bound on the spanning ratio for the special case where the empty convex shape is an arbitrary rectangle to $\sqrt{2} \cdot \left( 2 l/s + 1 \right)$, where $l$ and $s$ are the length of the long and short side of the rectangle.