,
Giuseppe Liotta
,
Maurizio Patrignani
,
Antonios Symvonis
,
Ioannis G. Tollis
Creative Commons Attribution 4.0 International license
We study a question that lies at the intersection of classical research subjects in Topological Graph Theory and Graph Drawing: Computing a drawing of a graph with a prescribed number of crossings on a given set S of points, while ensuring that its curve complexity (i.e., maximum number of bends per edge) is bounded by a constant. We focus on trees: Let T be a tree, ϑ(T) be its thrackle number, and χ be any integer in the interval [0,ϑ(T)]. In the tangling phase we compute a topological linear embedding of T with ϑ(T) edge crossings and a constant number of spine traversals. In the untangling phase we remove edge crossings without increasing the spine traversals until we reach χ crossings. The computed linear embedding is used to construct a drawing of T on S with χ crossings and constant curve complexity. Our approach gives rise to an O(n²)-time algorithm for general trees and an O(n log n)-time algorithm for paths. We also adapt the approach to compute RAC drawings, i.e. drawings where the angles formed at edge crossings are π/2.
@InProceedings{dibattista_et_al:LIPIcs.GD.2025.8,
author = {Di Battista, Giuseppe and Liotta, Giuseppe and Patrignani, Maurizio and Symvonis, Antonios and Tollis, Ioannis G.},
title = {{Tangling and Untangling Trees on Point-Sets}},
booktitle = {33rd International Symposium on Graph Drawing and Network Visualization (GD 2025)},
pages = {8:1--8:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-403-1},
ISSN = {1868-8969},
year = {2025},
volume = {357},
editor = {Dujmovi\'{c}, Vida and Montecchiani, Fabrizio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.GD.2025.8},
URN = {urn:nbn:de:0030-drops-249947},
doi = {10.4230/LIPIcs.GD.2025.8},
annote = {Keywords: Tree drawings, Prescribed edge crossings, Thrackle, Curve complexity, Point-set embeddings, RAC drawings, Topological linear embeddings}
}