Convex drawings of hierarchical planar graphs and clustered planar graphs

  • Authors:
  • Seok-Hee Hong;Hiroshi Nagamochi

  • Affiliations:
  • School of Information Technologies, University of Sydney, Australia;Dept. of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Japan

  • Venue:
  • Journal of Discrete Algorithms
  • Year:
  • 2010

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Abstract

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.