Abstract:AbatractWe show that nondegenerate Delaunay triangulations satisfy a combinatorial property called ltoughness. A graph with set of sites S is l-tough if for any set P E S, c(S -P) 5 IS], where c(S -P) is the number of components of the subgraph induced by the complement of P and ]P] is the number of sites in P. We also show that, under the same conditions, the number of interior, components of S -P ia at most IPI -2. These appear to be the first nontrivial properties of a purely combinatorial nature to be esta… Show more
“…In the proof of the next result we will use the following result of Dillencourt [11]: Let Γ be a Delaunay drawing with possibly degenerate vertex set V . Add, if necessary, edges to Γ to obtain a triangulation of V .…”
Section: Approximate Delaunay Drawingsmentioning
confidence: 99%
“…Note that this immediately implies that the graph with the planar embedding of Fig. 4 does not admit an embedding preserving Delaunay drawing [11] since removing vertices a, b, c and d yields three connected components.…”
We introduce and study a generalization of the well-known region of influence proximity drawings, called (ε 1 , ε 2 )-proximity drawings. Intuitively, given a definition of proximity and two real numbers ε 1 ≥ 0 and ε 2 ≥ 0, an (ε 1 , ε 2 )-proximity drawing of a graph is a planar straight-line drawing Γ such that: (i) for every pair of adjacent vertices u, v, their proximity region "shrunk" by the multiplicative factor 1 1+ε 1 does not contain any vertices of Γ; (ii) for every pair of non-adjacent vertices u, v, their proximity region "expanded" by the factor (1 + ε 2 ) contains some vertices of Γ other than u and v. In particular, the locations of the vertices in such a drawing do not always completely determine which edges must be present/absent, giving us some freedom of choice. We show that this generalization significantly enlarges the family of representable planar graphs for relevant definitions of proximity drawings, including Gabriel drawings, Delaunay drawings, and β-drawings, even for arbitrarily small values of ε 1 and ε 2 . We also study the extremal case of (0, ε 2 )-proximity drawings, which generalize the well-known weak proximity drawing paradigm.
“…In the proof of the next result we will use the following result of Dillencourt [11]: Let Γ be a Delaunay drawing with possibly degenerate vertex set V . Add, if necessary, edges to Γ to obtain a triangulation of V .…”
Section: Approximate Delaunay Drawingsmentioning
confidence: 99%
“…Note that this immediately implies that the graph with the planar embedding of Fig. 4 does not admit an embedding preserving Delaunay drawing [11] since removing vertices a, b, c and d yields three connected components.…”
We introduce and study a generalization of the well-known region of influence proximity drawings, called (ε 1 , ε 2 )-proximity drawings. Intuitively, given a definition of proximity and two real numbers ε 1 ≥ 0 and ε 2 ≥ 0, an (ε 1 , ε 2 )-proximity drawing of a graph is a planar straight-line drawing Γ such that: (i) for every pair of adjacent vertices u, v, their proximity region "shrunk" by the multiplicative factor 1 1+ε 1 does not contain any vertices of Γ; (ii) for every pair of non-adjacent vertices u, v, their proximity region "expanded" by the factor (1 + ε 2 ) contains some vertices of Γ other than u and v. In particular, the locations of the vertices in such a drawing do not always completely determine which edges must be present/absent, giving us some freedom of choice. We show that this generalization significantly enlarges the family of representable planar graphs for relevant definitions of proximity drawings, including Gabriel drawings, Delaunay drawings, and β-drawings, even for arbitrarily small values of ε 1 and ε 2 . We also study the extremal case of (0, ε 2 )-proximity drawings, which generalize the well-known weak proximity drawing paradigm.
“…In our study, we generally use the edges of an approximate Delaunay triangulation of the set of points. This edge set has the nice property that it is not too dense, but still captures well the structure of the point set and it contains a perfect matching (see Akl [2] and Dillencourt [21] ).…”
We make several observations on the implementation of Edmonds' blossom algorithm for solving minimum-weight perfectmatching problems and we present computational results for geometric problem instances ranging in size from 1,000 nodes up to 5,000,000 nodes. A key feature in our implementation is the use of multiple search trees with an individual dual-change ⑀ for each tree. As a benchmark of the algorithm's performance, solving a 100,000-node geometric instance on a 200 Mhz Pentium-Pro computer takes approximately 3 minutes.
“…Given a point set P and a class C of geometric objects, the maximum C -matching problem is to compute a subclass C ′ of C of maximum cardinality such that no point from P belongs to more than one element of C ′ and for each C ∈ C ′ , there are exactly two points from P which lie inside C. Dillencourt [4] proved that every point set admits a perfect circle-matching.Ábrego et al [5] studied the isothetic square matching problem. Bereg et al concentrated on matching points using axis-aligned squares and rectangles [6].…”
Given a point set P and a class C of geometric objects, G C (P) is a geometric graph with vertex set P such that any two vertices p and q are adjacent if and only if there is some C ∈ C containing both p and q but no other points from P. We study G ▽ (P) graphs where ▽ is the class of downward equilateral triangles (ie. equilateral triangles with one of their sides parallel to the x-axis and the corner opposite to this side below that side). For point sets in general position, these graphs have been shown to be equivalent to half-Θ 6 graphs and TD-Delaunay graphs.The main result in our paper is that for point sets P in general position, G ▽ (P) always contains a matching of size at leastand this bound is tight. We also give some structural properties of G (P) graphs, where is the class which contains both upward and downward equilateral triangles. We show that for point sets in general position, the block cut point graph of G (P) is simply a path. Through the equivalence of G (P) graphs with Θ 6 graphs, we also derive that any Θ 6 graph can have at most 5n − 11 edges, for point sets in general position.
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