Mixed Upward Planarization – Fast and Robust
In a mixed upward drawing of a graph G = (V,E) all directed edges ED ⊆ E are represented by monotonically increasing curves. Mixed upward drawings arise in applications like UML diagrams where such edges denote a hierarchical structure. The mixed upward planarization is an important subtask for computing such drawings. We outline a fast and simple heuristic approach that provides a good quality and can be applied to larger graphs as before in reasonable time. Unlike other Sugiyama-style  approaches, the quality is comparable to the GT based approach  even if there are only few directed edges. Furthermore, the new approach is particularly suitable for extensions like clustering and swimlanes.
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