Parallelism and rectangularity

This chapter treats parallelism and rectangularity together, because they are naturally connected: If one line is orthogonal to a second line and this second line in turn is again orthogonal to a third line, the third line and the first line will automatically be parallel. Thus, some constraints may be independent and some may be highly dependent on each other. These dependencies become very important when hand-drawn sketches and schemes are automatically analyzed. All kinds of diagrams, including UML graphs, show strong preference for orthogonality and parallelism. In this world, also connectivity plays an important role, so that this relation is discussed in this chapter as well. Parallelism alone, without connecting orthogonal lines, needs very close proximity. Therefore, this chapter defines a separate operation for this Gestalt organization law.