Planar Preprocessing for Spring Embedders

Abstract

Spring embedders are conceptually simple and produce straight-line drawings with an undeniable aesthetic appeal, which explains their prevalence when it comes to automated graph drawing. However, when drawing planar graphs, spring embedders often produce non-plane drawings, as edge crossings do not factor into the objective function being minimized. On the other hand, there are fairly straight-forward algorithms for creating plane straight-line drawings for planar graphs, but the resulting layouts generally are not aesthetically pleasing, as vertices are often grouped in small regions and edges lengths can vary dramatically. It is known that the initial layout influences the output of a spring embedder, and yet a random layout is nearly always the default. We study the effect of using various plane initial drawings as an inputs to a spring embedder, measuring the percent improvement in reducing crossings and in increasing node separation, edge length uniformity, and angular resolution.