Convex Drawing Research Articles

Convex Grid Drawings of Plane Graphs with Pentagonal Contours on <i>O</i>(<i>n</i><sup>2</sup>) Grids

In a convex grid drawing of a plane graph, all edges are drawn as straight-line segments without any edge-intersection, all vertices are put on grid points and all facial cycles are drawn as convex polygons. A plane graph G has a convex drawing if and only if G is internally triconnected, and an internally triconnected plane graph G has a convex grid drawing on an (n-1)×(n-1) grid if either G is triconnected or the triconnected component decomposition tree T(G) of G has two or three leaves, where n is the number of vertices in G. An internally triconnected plane graph G has a convex grid drawing on a 2n×2n grid if T(G) has exactly four leaves. Furthermore, an internally triconnected plane graph G has a convex grid drawing on a 6n×n2 grid if T(G) has exactly five leaves. In this paper, we show that an internally triconnected plane graph G has a convex grid drawing on a 20n×16n grid if T(G) has exactly five leaves. We also present an algorithm to find such a drawing in linear time. This is the first algorithm that finds a convex grid drawing of such a plane graph G in a grid of O(n2) size.

Analysis of Railway Network Accessibility in the Yangtze River Delta Urban Agglomeration Based on Space Syntax

The study abstracts the 26 main cities of urban agglomeration in Yangtze River Delta as convex space, and constructs a convex drawing based on the passenger railway network of 2008, 2018, and 2030 in Yangtze River Delta with Depthmap. After calculating the network integration and intelligibility, the relationship between the development of the railway network and the spatial structure change of urban agglomeration in the Yangtze River Delta are analysed and it finds that: (1) The development of the ordinary railway network is relatively slow and uncoordinated, while the high-speed railway network is developing rapidly and co-ordinately. (2) The spatial layout of railway network accessibility develops from the circle structure to the point-axis structure, and then to the multi-core structure. As a whole, the overall network development becomes increasingly mature and balanced, but the small-scale networks of local area become more differentiated. (3) As the development of multiple cores, the network accessibility has changed from low-level equilibrium period to an unbalanced period and then to a high-level equilibrium period.

Aligned Drawings of Planar Graphs

Let $G$ be a graph that is topologically embedded in the plane and let $\mathcal A$ be an arrangement of pseudolines intersecting the drawing of $G$. An aligned drawing of $G$ and $\mathcal A$ is a planar polyline drawing $\Gamma$ of $G$ with an arrangement $A$ of lines so that $\Gamma$ and $A$ are homeomorphic to $G$ and $\mathcal A$. We show that if $\mathcal A$ is stretchable and every edge $e$ either entirely lies on a pseudoline or it has at most one intersection with $\mathcal A$, then $G$ and $\mathcal A$ have a straight-line aligned drawing. In order to prove this result, we strengthen a result of Da Lozzo et al. [Da Lozzo et al. GD 2016], and prove that a planar graph $G$ and a single pseudoline $\mathcal L$ have an aligned drawing with a prescribed convex drawing of the outer face. We also study the less restrictive version of the alignment problem with respect to one line, where only a set of vertices is given and we need to determine whether they can be collinear. We show that the problem is $\mathcal{NP}$-complete but fixed-parameter tractable.

On the Maximum Crossing Number

Research about crossings is typically about minimization. In this paper, we consider maximizing the number of crossings over all possible ways to draw a given graph in the plane. Alpert et al. [Electron. J. Combin., 2009] conjectured that any graph has a convex straight-line drawing, that is, a drawing with vertices in convex position, that maximizes the number of edge crossings. We disprove this conjecture by constructing a planar graph on twelve vertices that admits a non-convex drawing with more crossings than any convex drawing. Bald et al. [Proc. COCOON, 2016] showed that it is NP-hard to compute the maximum number of crossings of a geometric graph and that the weighted geometric case is NP-hard to approximate. We strengthen these results by showing hardness of approximation even for the unweighted geometric case. We also prove that the unweighted topological case is NP-hard.

On orthogonally convex drawings of plane graphs

We investigate the bend-minimization problem with respect to a new drawing style called an orthogonally convex drawing, which is an orthogonal drawing with an additional requirement that each inner face is drawn as an orthogonally convex polygon. For the class of biconnected plane graphs of maximum degree 3, we present a necessary and sufficient condition for the existence of a no-bend orthogonally convex drawing, which in turn, enables a linear time algorithm to check and construct such a drawing if one exists. We also develop a flow network formulation for bend-minimization in orthogonally convex drawings, yielding a polynomial time solution for the problem. An interesting application of our orthogonally convex drawing technique is to characterize internally triangulated plane graphs that admit floorplans using only orthogonally convex modules subject to given orthogonally convex boundary constraints.

Star-Shaped and L-Shaped Orthogonal Drawings

An orthogonal drawing of a plane graph $G$ is a planar drawing of $G$, denoted by $D(G)$, such that each vertex of $G$ is drawn as a point on the plane, and each edge of $G$ is drawn as a sequence of horizontal and vertical line segments with no crossings. An orthogonal polygon $P$ is called orthogonally convex if the intersection of any horizontal or vertical line $L$ and $P$ is either a single line segment or empty. An orthogonal drawing $D(G)$ is called orthogonally convex if all of its internal faces are orthogonally convex polygons. An orthogonal polygon $P$ is called a star-shaped polygon if there is a point $p\in P$ such that the entire $P$ is visible from $p$. An orthogonal drawing $D(G)$ is called a star-shaped orthogonal drawing (SSOD) if all of its internal faces are star-shaped polygons. Every SSOD is an orthogonally convex drawing, but the reverse is not true. SSOD is visually more appealing than orthogonally convex drawings. Recently, Chang et al. gave a necessary and sufficient condition for a plane graph to have an orthogonally convex drawing. In this paper, we show that if $G$ satisfies the same condition given by Chang et al., it not only has an orthogonally convex drawing, but also a SSOD, which can be constructed in linear time. An orthogonal drawing $D(G)$ is called an $L$-shaped drawing if each face of $D(G)$ is an $L$-shaped polygon. In this paper we also show that an $L$-shaped orthogonal drawing can be constructed in $O(n)$ time. The same algorithmic technique is used for solving both problems. It is based on regular edge labeling and is quite different from the methods used in previous results.

Extending Convex Partial Drawings of Graphs

Given a plane graph G (i.e., a planar graph with a fixed planar embedding and outer face) and a biconnected subgraph $$G^{\prime }$$Gź with a fixed planar straight-line convex drawing, we consider the question whether this drawing can be extended to a planar straight-line drawing of G. We characterize when this is possible in terms of simple necessary conditions, which we prove to be sufficient. This also leads to a linear-time testing algorithm. If a drawing extension exists, one can be computed in the same running time.

Survey on Convex Drawing of Planar Graph

This paper presented study on convex drawing of planar graph. In graph theory, a planar graph is a graph that can be embedded in the plane. A planar graph is one that can be drawn on a plane in such a way that there are no “edge crossings,” i.e. edges intersect only at their common vertices. Convex polygon has all interior angles less than or equal to 180°. A graph is called a convex drawing if every facial cycle (face) is drawn as a convex polygon. In a convex drawing of a planar graph, all edges are drawn by straight line segments in such a way that every face boundary in a convex polygon. This paper describes some of the recent works on convex drawing on planar graph.

Minimum-segment convex drawings of 3-connected cubic plane graphs

A convex drawing of a plane graph G is a plane drawing of G, where each vertex is drawn as a point, each edge is drawn as a straight line segment and each face is drawn as a convex polygon. A maximal segment is a drawing of a maximal set of edges that form a straight line segment. A minimum-segment convex drawing of G is a convex drawing of G where the number of maximal segments is the minimum among all possible convex drawings of G. In this paper, we present a linear-time algorithm to obtain a minimum-segment convex drawing Γ of a 3-connected cubic plane graph G of n vertices, where the drawing is not a grid drawing. We also give a linear-time algorithm to obtain a convex grid drawing of G on an $(\frac{n}{2}+1)\times(\frac {n}{2}+1)$ grid with at most s n +1 maximal segments, where $s_{n}=\frac{n}{2}+3$ is the lower bound on the number of maximal segments in a convex drawing of G.

CONVEX DRAWINGS OF INTERNALLY TRICONNECTED PLANE GRAPHS ON O(n2) GRIDS

In a convex grid drawing of a plane graph, every edge is drawn as a straight-line segment without any edge-intersection, every vertex is located at a grid point, and every facial cycle is drawn as a convex polygon. A plane graph G has a convex drawing if and only if G is internally triconnected. It has been known that an internally triconnected plane graph G of n vertices has a convex grid drawing on a grid of O(n3) area if the triconnected component decomposition tree of G has at most four leaves. In this paper, we improve the area bound O(n3) to O(n2), which is optimal up to a constant factor. More precisely, we show that G has a convex grid drawing on a 2n × 4n grid. We also present an algorithm to find such a drawing in linear time.

An algorithm for constructing star-shaped drawings of plane graphs

A straight-line planar drawing of a plane graph is called a convex drawing if every facial cycle is drawn as a convex polygon. Convex drawings of graphs is a well-established aesthetic in graph drawing, however not all planar graphs admit a convex drawing. Tutte [W.T. Tutte, Convex representations of graphs, Proc. of London Math. Soc. 10 (3) (1960) 304–320] showed that every triconnected plane graph admits a convex drawing for any given boundary drawn as a convex polygon. Thomassen [C. Thomassen, Plane representations of graphs, in: Progress in Graph Theory, Academic Press, 1984, pp. 43–69] gave a necessary and sufficient condition for a biconnected plane graph with a prescribed convex boundary to have a convex drawing. In this paper, we initiate a new notion of star-shaped drawing of a plane graph as a straight-line planar drawing such that each inner facial cycle is drawn as a star-shaped polygon, and the outer facial cycle is drawn as a convex polygon. A star-shaped drawing is a natural extension of a convex drawing, and a new aesthetic criteria for drawing planar graphs in a convex way as much as possible. We give a sufficient condition for a given set A of corners of a plane graph to admit a star-shaped drawing whose concave corners are given by the corners in A, and present a linear time algorithm for constructing such a star-shaped drawing.

Convex drawings of hierarchical planar graphs and clustered planar graphs

In this paper, we present results on convex drawings of hierarchical graphs and clustered graphs. A convex drawing is a planar straight-line drawing of a plane graph, where every facial cycle is drawn as a convex polygon. Hierarchical graphs and clustered graphs are useful graph models with structured relational information. Hierarchical graphs are graphs with layering structures; clustered graphs are graphs with recursive clustering structures. We first present the necessary and sufficient conditions for a hierarchical plane graph to admit a convex drawing. More specifically, we show that the necessary and sufficient conditions for a biconnected plane graph due to Thomassen [C. Thomassen, Plane representations of graphs, in: J.A. Bondy, U.S.R. Murty (Eds.), Progress in Graph Theory, Academic Press, 1984, pp. 43–69] remains valid for the case of a hierarchical plane graph. We then prove that every internally triconnected clustered plane graph with a completely connected clustering structure admits a “fully convex drawing,” a planar straight-line drawing such that both clusters and facial cycles are drawn as convex polygons. We also present algorithms to construct such convex drawings of hierarchical graphs and clustered graphs.

A Linear-Time Algorithm for Symmetric Convex Drawings of Internally Triconnected Plane Graphs

Symmetry is one of the most important aesthetic criteria in Graph Drawing which can reveal the hidden structure in the graph. Convex drawing is a straight-line drawing where every facial cycle is drawn as a convex polygon. In this paper, we prove that given an internally triconnected plane graph with symmetries, there exists a convex drawing of the graph which displays the given symmetries. We present a linear-time algorithm for constructing symmetric convex drawings of internally triconnected planar graphs. This is an extension of a classical result due to Tutte (Proc. Lond. Math. Soc. 10(3):304–320, 1960; Proc. Lond. Math. Soc. 13:743–768, 1963) who proved that every triconnected plane graph with a given convex polygon as a boundary admits a convex drawing. Note that Tutte’s barycenter mapping method can be implemented in O(n 1.5) time and O(nlog n) space at best (Lipton et al. in SIAM J. Numer. Anal. 16:346–358, 1979). Our divide and conquer algorithm explicitly exploits the fundamental properties of symmetric drawing, which consists of congruent drawings of isomorphic subgraphs. We first find an isomorphic subgraph of a given symmetric plane graph, and compute an angle-constrained convex drawing of the subgraph. Finally, a symmetric convex drawing of the given graph is constructed by merging repetitive copies of the congruent drawings of isomorphic subgraphs. For this purpose, we define a new problem of angle-constrained convex drawing of plane graphs, where some of outer vertices have angle constraints. Our results also imply that there is a linear-time algorithm that constructs maximally symmetric convex drawings of triconnected planar graphs. Previous algorithm (Hong et al. in Discrete Comput. Geom. 36:283–311, 2006) constructs symmetric drawings of triconnected planar graphs with straight-lines.

Convex drawings of graphs with non-convex boundary constraints

In this paper, we study a new problem of convex drawing of planar graphs with non-convex boundary constraints, and call a drawing in which every inner-facial cycle is drawn as a convex polygon an inner-convex drawing. It is proved that every triconnected plane graph with the boundary fixed with a star-shaped polygon whose kernel has a positive area admits an inner-convex drawing. We also prove that every four-connected plane graph whose boundary is fixed with a crown-shaped polygon admits an inner-convex drawing. We present linear time algorithms to construct inner-convex drawings for both cases.

Barycentric systems and stretchability

Using a general resolution of barycentric systems we give a generalization of Tutte's theorem on convex drawing of planar graphs. We deduce a characterization of the edge coverings into pairwise non-crossing paths which are stretchable: such a system is stretchable if and only if each subsystem of at least two paths has at least three free vertices (vertices of the outer face of the induced subgraph which are internal to none of the paths of the subsystem). We also deduce that a contact system of pseudo-segments is stretchable if and only if it is extendible.

CONVEX DRAWINGS OF PLANE GRAPHS OF MINIMUM OUTER APICES

In a convex drawing of a plane graph G, every facial cycle of G is drawn as a convex polygon. A polygon for the outer facial cycle is called an outer convex polygon. A necessary and sufficient condition for a plane graph G to have a convex drawing is known. However, it has not been known how many apices of an outer convex polygon are necessary for G to have a convex drawing. In this paper, we show that the minimum number of apices of an outer convex polygon necessary for G to have a convex drawing is, in effect, equal to the number of leaves in a triconnected component decomposition tree of a new graph constructed from G, and that a convex drawing of G having the minimum number of apices can be found in linear time.

Incremental Convex Planarity Testing

An important class of planar straight-line drawings of graphs are convex drawings, in which all the faces are drawn as convex polygons. A planar graph is said to be convex planar if it admits a convex drawing. We give a new combinatorial characterization of convex planar graphs based on the decomposition of a biconnected graph into its triconnected components. We then consider the problem of testing convex planarity in an incremental environment, where a biconnected planar graph is subject to on-line insertions of vertices and edges. We present a data structure for the on-line incremental convex planarity testing problem with the following performance, where n denotes the current number of vertices of the graph: (strictly) convex planarity testing takes O(1) worst-case time, insertion of vertices takes O(log n) worst-case time, insertion of edges takes O(log n) amortized time, and the space requirement of the data structure is O(n).