Linear Size Planar Manhattan Network for Convex Point Sets

Let $G = (V, E)$ be an edge-weighted geometric graph such that every edge is horizontal or vertical. The weight of an edge $uv \in E$ is its length. Let $W_G (u,v)$ denote the length of a shortest path between a pair of vertices $u$ and $v$ in $G$. The graph $G$ is said to be a Manhattan network for a given point set $P$ in the plane if $P \subseteq V$ and $\forall p,q \in P$, $W_G (p,q)=|pq|_1$. In addition to $P$, graph $G$ may also include a set $T$ of Steiner points in its vertex set $V$. In the Manhattan network problem, the objective is to construct a Manhattan network of small size for a set of $n$ points. This problem was first considered by Gudmundsson et al.\cite{gudmundsson2007small}. They give a construction of a Manhattan network of size $\Theta(n \log n)$ for general point set in the plane. We say a Manhattan network is planar if it can be embedded in the plane without any edge crossings. In this paper, we construct a linear size planar Manhattan network for convex point set in linear time using $\mathcal{ O}(n)$ Steiner points. We also show that, even for convex point set, the construction in Gudmundsson et al. \cite{gudmundsson2007small} needs $\Omega (n \log n)$ Steiner points and the network may not be planar.