# Polyline Drawings with Topological Constraints

Let G be a simple topological graph and let Γ be a polyline drawing of G. We say that Γ partially preserves the topology of G if it has the same external boundary, the same rotation system, and the same set of crossings as G. Drawing Γ fully preserves the topology of G if the planarization of G and the planarization of Γ have the same planar embedding. We show that if the set of crossing-free edges of G forms a connected spanning subgraph, then G admits a polyline drawing that partially preserves its topology and that has curve complexity at most three (i.e., at most three bends per edge). If, however, the set of crossing-free edges of G is not a connected spanning subgraph, the curve complexity may be Ω(√(n)). Concerning drawings that fully preserve the topology, we show that if G has skewness k, it admits one such drawing with curve complexity at most 2k; for skewness-1 graphs, the curve complexity can be reduced to one, which is a tight bound. We also consider optimal 2-plane graphs and discuss trade-offs between curve complexity and crossing angle resolution of drawings that fully preserve the topology.

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