Overview of the layout phases

The task of aiSee is to parse a graph specification, calculate a layout according to the layout algorithm chosen, and draw the resulting layout in a window. The GDL specification given as input to aiSee is a readable ASCII text. The output window can be used to browse through the graph, shrink or magnify the graph, fold parts of the graph, and export the graph to a bitmap, PostScript or SVG file. Folding operations potentially result in a new layout of the graph. The layout can be extensively influenced by edge, node and graph attributes or by different layout algorithms. aiSee offers force-directed and hierarchical layout schemes.

Parsing phase

The first phase is to parse the GDL specification and construct internal data structures representing the graph. The GDL specification may contain attributes denoting initially folded parts of the graph.

Folding phase

aiSee offers various ways of grouping graph elements. Folding operations enable the graph to be inspected in a more efficient manner. Folding the unimportant parts gives the more important parts more space for visualization. Folding parts of the graph also improves aiSee's performance. It should be noted that nested foldings are possible.

In graph specifications, the folding of regions or subgraphs may interfere with the hiding of edges. In this case, first the summary node of the folded region or subgraph is calculated, followed by hiding the edges.

Layout phases

• Hierarchical Layout
• Rank assignment
• Crossing reduction
• Coordinate calculation
• Edge bending
• Force-directed layout
• Drawing phase
• Message characters

Last modified on 6 May 2002 by webmaster. © 2000-2002 AbsInt.
URL: http://www.aisee.com/manual/unix/52.htm

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