Inhomogeneous Force-Directed Layout Algorithms in the - CiteSeer

Inhomogeneous Force-Directed Layout Algorithms in the Visualisation Pipeline: From Layouts to Visualisations Neville Churcher Warwick Irwin Carl Cook Software Visualistion Group, Department of Computer Science, University of Canterbury, Private Bag 4800, Christchurch, New Zealand E-mail: fneville,wal,c.cookg@cosc.canterbury.ac.nz Abstract The visualisation pipeline approach is a flexible and extensible technique for generating visualisations. The basic pipeline functions involve the capture and representation of data, the computation of geometry and the presentation of visual output. Data is rep- resented in XML at each stage

and is successively transformed, typically by XSLT transformations, as it moves through the pipeline. A force-directed lay- out engine, Angle is one of the major components in the computation of 2D and 3D geometry. In this paper, we describe inhomogeneous force models and their implementation in Angle. These allow a richer variety of properties and relationships of the under- lying graph and application domain to be included in the visualisation. We present examples from our software visualisation research. 1 Introduction Force-directed layout techniques, also known as spring embedders, (Eades 1983, Eades 1984, Di Bat- tista, Eades, Tamassia & Tollis 1999) are a reliable general-purpose tool for graph layout applications. Although other techniques may be capable of deliv- ering superior results for particular classes of graphs, force-directed methods have found application in a wide range of areas. In our work, we require layout algorithms which can reliably provide a satisfactory layout when pre- sented with an unknown graph. It is more important that our layouts be good enough all the time" than great some of the time". Force-directed methods generally exhibit smooth convergence to the nal lay- out con guration, making them particularly suitable for layouts which are presented dynamically to users via a graphical user interface. The remainder of the paper is structured as fol- lows. In the next section, we outline our visualisa- tion pipeline approach and describe the r^ole of An- gle (Churcher & Creek 2001), our layout engine. We introduce inhomogeneous force models in Section 3 and discuss our approach and its implementation in Section 4. We illustrate our approach by presenting some examples of its application in Section 5. Finally, our conclusions and discussion of work in progress are presented in Section 6. Copyright c©2004, Australian Computer Society, Inc. This pa- per appeared at the Australasian Symposium on Information Visualisation, Christchurch, 2004. Conferences in Research and Practice in Information Technology, Vol. ??. Neville Churcher and Clare Churcher, Ed. Reproduction for academic, not-for pro t purposes permitted provided this text is included. 2 Layout in the visualisation pipeline The conventional visualisation pipeline (Schroeder, Martin & Lorensen 1998, for example) consists of three basic phases: data capture/generation & pro- cessing; computation of geometry and rendering of the resulting visualisation. Our recent work in information and software vi- sualisation (Churcher, Keown & Irwin 1999, Irwin & Churcher 2002, Churcher, Irwin & Kriz 2003, Irwin & Churcher 2003) involves a...

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