,
Christian Howard
Creative Commons Attribution 4.0 International license
We describe a promising approach to efficiently morph spherical graphs, extending earlier approaches of Awartani and Henderson [Trans. AMS 1987] and Kobourov and Landis [JGAA 2006]. Specifically, we describe two methods to morph shortest-path triangulations of the sphere by moving their vertices along longitudes into the southern hemisphere; we call a triangulation sinkable if such a morph exists. Our first method generalizes a longitudinal shelling construction of Awartani and Henderson; a triangulation is sinkable if a specific orientation of its dual graph is acyclic. We describe a simple polynomial-time algorithm to find a longitudinally shellable rotation of a given spherical triangulation, if one exists; we also construct a spherical triangulation that has no longitudinally shellable rotation. Our second method is based on a linear-programming characterization of sinkability. By identifying its optimal basis, we show that this linear program can be solved in O(n^{ω/2}) time, where ω is the matrix-multiplication exponent, assuming the underlying linear system is non-singular. Finally, we pose several conjectures and describe experimental results that support them.
@InProceedings{erickson_et_al:LIPIcs.SoCG.2025.47,
author = {Erickson, Jeff and Howard, Christian},
title = {{Shelling and Sinking Graphs on the Sphere}},
booktitle = {41st International Symposium on Computational Geometry (SoCG 2025)},
pages = {47:1--47:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-370-6},
ISSN = {1868-8969},
year = {2025},
volume = {332},
editor = {Aichholzer, Oswin and Wang, Haitao},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2025.47},
URN = {urn:nbn:de:0030-drops-231996},
doi = {10.4230/LIPIcs.SoCG.2025.47},
annote = {Keywords: morphing, planar graphs, spherical graph drawing, longitudinal shelling}
}