We consider path planning for a rigid spatial robot moving amidst polyhedral obstacles. Our robot is either a rod or a ring. Being axially-symmetric, their configuration space is R^3 x S^2 with 5 degrees of freedom (DOF). Correct, complete and practical path planning for such robots is a long standing challenge in robotics. While the rod is one of the most widely studied spatial robots in path planning, the ring seems to be new, and a rare example of a non-simply-connected robot. This work provides rigorous and complete algorithms for these robots with theoretical guarantees. We implemented the algorithms in our open-source Core Library. Experiments show that they are practical, achieving near real-time performance. We compared our planner to state-of-the-art sampling planners in OMPL [Sucan et al., 2012]. Our subdivision path planner is based on the twin foundations of epsilon-exactness and soft predicates. Correct implementation is relatively easy. The technical innovations include subdivision atlases for S^2, introduction of Sigma_2 representations for footprints, and extensions of our feature-based technique for "opening up the blackbox of collision detection".
@InProceedings{hsu_et_al:LIPIcs.SoCG.2019.43, author = {Hsu, Ching-Hsiang and Chiang, Yi-Jen and Yap, Chee}, title = {{Rods and Rings: Soft Subdivision Planner for R^3 x S^2}}, booktitle = {35th International Symposium on Computational Geometry (SoCG 2019)}, pages = {43:1--43:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-104-7}, ISSN = {1868-8969}, year = {2019}, volume = {129}, editor = {Barequet, Gill and Wang, Yusu}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2019.43}, URN = {urn:nbn:de:0030-drops-104477}, doi = {10.4230/LIPIcs.SoCG.2019.43}, annote = {Keywords: Algorithmic Motion Planning, Subdivision Methods, Resolution-Exact Algorithms, Soft Predicates, Spatial Rod Robots, Spatial Ring Robots} }