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Given n line segments in the plane, do they form the edge set of a weakly simple polygon; that is, can the segment endpoints be perturbed by at most epsilon, for any epsilon > 0, to obtain a simple polygon? While the analogous question for simple polygons can easily be answered in O(n log n) time, we show that it is NP-complete for weakly simple polygons. We give O(n)-time algorithms in two special cases: when all segments are collinear, or the segment endpoints are in general position. These results extend to the variant in which the segments are directed, and the counterclockwise traversal of a polygon should follow the orientation. We study related problems for the case that the union of the n input segments is connected. (i) If each segment can be subdivided into several segments, find the minimum number of subdivision points to form a weakly simple polygon. (ii) If new line segments can be added, find the minimum total length of new segments that creates a weakly simple polygon. We give worst-case upper and lower bounds for both problems.
@InProceedings{akitaya_et_al:LIPIcs.ISAAC.2016.10,
author = {Akitaya, Hugo A. and T\'{o}th, Csaba D.},
title = {{Reconstruction of Weakly Simple Polygons from their Edges}},
booktitle = {27th International Symposium on Algorithms and Computation (ISAAC 2016)},
pages = {10:1--10:13},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-026-2},
ISSN = {1868-8969},
year = {2016},
volume = {64},
editor = {Hong, Seok-Hee},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2016.10},
URN = {urn:nbn:de:0030-drops-67795},
doi = {10.4230/LIPIcs.ISAAC.2016.10},
annote = {Keywords: simple polygon, line segment, geometric graph}
}