Given a set S of n points in the plane, we give an O(n log n)-time algorithm that constructs a plane t-spanner for S, with t ≈ 10, such that the degree of each point of S is bounded from above by 27, and the total edge length is proportional to the weight of a minimum spanning tree of S. Previously, no algorithms were known for constructing plane t-spanners of bounded degree.
Introduction.Givena set S of n points in the plane and a real number t > 1, a t-spanner for S is a graph G with vertex set S such that any two vertices u and v are connected by a path in G whose length is at most t · |uv|, where |uv| is the Euclidean distance between u and v. If this graph has O(n) edges, then it is a sparse approximation of the (dense) complete Euclidean graph on S.Many algorithms are known that compute t-spanners with O(n) edges [1], [2], [8], [20], [22],[24], [26] that have additional properties such as bounded degree [4], [6], small spanner diameter [4] (i.e., any two points are connected by a t-spanner path consisting of only a small number of edges), low weight [11], [13], [19] (i.e., the total length of all edges is proportional to the weight of a minimum spanning tree of S), planarity [3], [21], and fault-tolerance [10], [23]; see also the surveys [18] and [25]. All these algorithms compute t-spanners for any given constant t > 1. Observe that some properties are conflicting. For instance a spanner with constant degree cannot have spanner diameter o(log n).In this paper we consider the construction of plane t-spanners. A graph, whose vertices are points in R 2 with straight-line edges, is said to be plane, if no two edges intersect, except possibly at their endpoints. Obviously, in order for a t-spanner to be plane, t must be at least √ 2. It is known that the Delaunay triangulation is a t-spanner for t = 2π/(3 cos(π/6)), see [21]. Furthermore, Das and Joseph [12] showed that other plane graphs such as the minimum weight triangulation and the greedy triangulation are t-spanners, for some constant t. In 1992 Levcopoulos and Lingas [22] showed that, for