
444 CHAPTER 13. HIERARCHICAL DRAWING ALGORITHMS
Hong and Nikolov have proposed an extension to the Sugiyama framework for hierarchical
drawing of digraphs in 3D [HN05b, HN05a]. They introduced the convention of drawing the
digraph in a set of parallel planes, called walls, each containing a 2D hierarchical drawing
of a subgraph of the input digraph. The partition of the vertex set into walls is done
at a separate wall-assigning step applied after the layer-assignment step and before the
vertex-ordering step. Hong and Nikolov proposed and evaluated various wall-assignment
algorithms which partition the vertex set into walls according to different criteria. ...