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Documents authored by Yap, Chee

Document
Media Exposition
DOI: 10.4230/LIPIcs.SoCG.2022.69
Subdivision Methods for Sum-Of-Distances Problems: Fermat-Weber Point, n-Ellipses and the Min-Sum Cluster Voronoi Diagram (Media Exposition)

Authors: Ioannis Mantas, Evanthia Papadopoulou, Martin Suderland, and Chee Yap

Published in: LIPIcs, Volume 224, 38th International Symposium on Computational Geometry (SoCG 2022)

Abstract
Given a set P of n points, the sum of distances function of a point x is d_{P}(x) : = ∑_{p ∈ P} ||x - p||. Using a subdivision approach with soft predicates we implement and visualize approximate solutions for three different problems involving the sum of distances function in ℝ². Namely, (1) finding the Fermat-Weber point, (2) constructing n-ellipses of a given set of points, and (3) constructing the nearest Voronoi diagram under the sum of distances function, given a set of point clusters as sites.
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Ioannis Mantas, Evanthia Papadopoulou, Martin Suderland, and Chee Yap. Subdivision Methods for Sum-Of-Distances Problems: Fermat-Weber Point, n-Ellipses and the Min-Sum Cluster Voronoi Diagram (Media Exposition). In 38th International Symposium on Computational Geometry (SoCG 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 224, pp. 69:1-69:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{mantas_et_al:LIPIcs.SoCG.2022.69,
  author =	{Mantas, Ioannis and Papadopoulou, Evanthia and Suderland, Martin and Yap, Chee},
  title =	{{Subdivision Methods for Sum-Of-Distances Problems: Fermat-Weber Point, n-Ellipses and the Min-Sum Cluster Voronoi Diagram}},
  booktitle =	{38th International Symposium on Computational Geometry (SoCG 2022)},
  pages =	{69:1--69:6},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-227-3},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{224},
  editor =	{Goaoc, Xavier and Kerber, Michael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2022.69},
  URN =		{urn:nbn:de:0030-drops-160773},
  doi =		{10.4230/LIPIcs.SoCG.2022.69},
  annote =	{Keywords: Fermat point, geometric median, Weber point, Fermat distance, sum of distances, n-ellipse, multifocal ellipse, min-sum Voronoi diagram, cluster Voronoi diagram}
}
Document
DOI: 10.4230/LIPIcs.ESA.2021.54
Certified Approximation Algorithms for the Fermat Point and n-Ellipses

Authors: Kolja Junginger, Ioannis Mantas, Evanthia Papadopoulou, Martin Suderland, and Chee Yap

Published in: LIPIcs, Volume 204, 29th Annual European Symposium on Algorithms (ESA 2021)

Abstract
Given a set A of n points in ℝ^d with weight function w: A→ℝ_{> 0}, the Fermat distance function is φ(x): = ∑_{a∈A}w(a)‖x-a‖. A classic problem in facility location dating back to 1643, is to find the Fermat point x*, the point that minimizes the function φ. We consider the problem of computing a point x̃* that is an ε-approximation of x* in the sense that ‖x̃*-x*‖<ε. The algorithmic literature has so far used a different notion based on ε-approximation of the value φ(x*). We devise a certified subdivision algorithm for computing x̃*, enhanced by Newton operator techniques. We also revisit the classic Weiszfeld-Kuhn iteration scheme for x*, turning it into an ε-approximate Fermat point algorithm. Our second problem is the certified construction of ε-isotopic approximations of n-ellipses. These are the level sets φ^{-1}(r) for r > φ(x*) and d = 2. Finally, all our planar (d = 2) algorithms are implemented in order to experimentally evaluate them, using both synthetic as well as real world datasets. These experiments show the practicality of our techniques.
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Kolja Junginger, Ioannis Mantas, Evanthia Papadopoulou, Martin Suderland, and Chee Yap. Certified Approximation Algorithms for the Fermat Point and n-Ellipses. In 29th Annual European Symposium on Algorithms (ESA 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 204, pp. 54:1-54:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{junginger_et_al:LIPIcs.ESA.2021.54,
  author =	{Junginger, Kolja and Mantas, Ioannis and Papadopoulou, Evanthia and Suderland, Martin and Yap, Chee},
  title =	{{Certified Approximation Algorithms for the Fermat Point and n-Ellipses}},
  booktitle =	{29th Annual European Symposium on Algorithms (ESA 2021)},
  pages =	{54:1--54:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-204-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{204},
  editor =	{Mutzel, Petra and Pagh, Rasmus and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2021.54},
  URN =		{urn:nbn:de:0030-drops-146359},
  doi =		{10.4230/LIPIcs.ESA.2021.54},
  annote =	{Keywords: Fermat point, n-ellipse, subdivision, approximation, certified, algorithms}
}
Document
DOI: 10.4230/LIPIcs.SoCG.2019.43
Rods and Rings: Soft Subdivision Planner for R^3 x S^2

Authors: Ching-Hsiang Hsu, Yi-Jen Chiang, and Chee Yap

Published in: LIPIcs, Volume 129, 35th International Symposium on Computational Geometry (SoCG 2019)

Abstract
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".
Cite as

Ching-Hsiang Hsu, Yi-Jen Chiang, and Chee Yap. Rods and Rings: Soft Subdivision Planner for R^3 x S^2. In 35th International Symposium on Computational Geometry (SoCG 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 129, pp. 43:1-43:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@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-dev.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}
}
Document
DOI: 10.4230/LIPIcs.ESA.2018.73
Soft Subdivision Motion Planning for Complex Planar Robots

Authors: Bo Zhou, Yi-Jen Chiang, and Chee Yap

Published in: LIPIcs, Volume 112, 26th Annual European Symposium on Algorithms (ESA 2018)

Abstract
The design and implementation of theoretically-sound robot motion planning algorithms is challenging. Within the framework of resolution-exact algorithms, it is possible to exploit soft predicates for collision detection. The design of soft predicates is a balancing act between easily implementable predicates and their accuracy/effectivity. In this paper, we focus on the class of planar polygonal rigid robots with arbitrarily complex geometry. We exploit the remarkable decomposability property of soft collision-detection predicates of such robots. We introduce a general technique to produce such a decomposition. If the robot is an m-gon, the complexity of this approach scales linearly in m. This contrasts with the O(m^3) complexity known for exact planners. It follows that we can now routinely produce soft predicates for any rigid polygonal robot. This results in resolution-exact planners for such robots within the general Soft Subdivision Search (SSS) framework. This is a significant advancement in the theory of sound and complete planners for planar robots. We implemented such decomposed predicates in our open-source Core Library. The experiments show that our algorithms are effective, perform in real time on non-trivial environments, and can outperform many sampling-based methods.
Cite as

Bo Zhou, Yi-Jen Chiang, and Chee Yap. Soft Subdivision Motion Planning for Complex Planar Robots. In 26th Annual European Symposium on Algorithms (ESA 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 112, pp. 73:1-73:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{zhou_et_al:LIPIcs.ESA.2018.73,
  author =	{Zhou, Bo and Chiang, Yi-Jen and Yap, Chee},
  title =	{{Soft Subdivision Motion Planning for Complex Planar Robots}},
  booktitle =	{26th Annual European Symposium on Algorithms (ESA 2018)},
  pages =	{73:1--73:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-081-1},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{112},
  editor =	{Azar, Yossi and Bast, Hannah and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2018.73},
  URN =		{urn:nbn:de:0030-drops-95361},
  doi =		{10.4230/LIPIcs.ESA.2018.73},
  annote =	{Keywords: Computational Geometry, Algorithmic Motion Planning, Resolution-Exact Algorithms, Soft Predicates, Planar Robots with Complex Geometry}
}
Document
DOI: 10.4230/LIPIcs.SoCG.2016.68
Path Planning for Simple Robots using Soft Subdivision Search

Authors: Ching-Hsiang Hsu, John Paul Ryan, and Chee Yap

Published in: LIPIcs, Volume 51, 32nd International Symposium on Computational Geometry (SoCG 2016)

Abstract
The concept of resolution-exact path planning is a theoretically sound alternative to the standard exact algorithms, and provides much stronger guarantees than probabilistic or sampling algorithms. It opens the way for the introduction of soft predicates in the context of subdivision algorithm. Taking a leaf from the great success of the Probabilistic Road Map (PRM) framework, we formulate an analogous framework for subdivision, called Soft Subdivision Search (SSS). In this video, we illustrate the SSS framework for a trio of simple planar robots: disc, triangle and 2-links. These robots have, respectively, 2, 3 and 4 degrees of freedom. Our 2-link robot can also avoid self-crossing. These algorithms operate in realtime and are relatively easy to implement.
Cite as

Ching-Hsiang Hsu, John Paul Ryan, and Chee Yap. Path Planning for Simple Robots using Soft Subdivision Search. In 32nd International Symposium on Computational Geometry (SoCG 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 51, pp. 68:1-68:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{hsu_et_al:LIPIcs.SoCG.2016.68,
  author =	{Hsu, Ching-Hsiang and Ryan, John Paul and Yap, Chee},
  title =	{{Path Planning for Simple Robots using Soft Subdivision Search}},
  booktitle =	{32nd International Symposium on Computational Geometry (SoCG 2016)},
  pages =	{68:1--68:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-009-5},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{51},
  editor =	{Fekete, S\'{a}ndor and Lubiw, Anna},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2016.68},
  URN =		{urn:nbn:de:0030-drops-59607},
  doi =		{10.4230/LIPIcs.SoCG.2016.68},
  annote =	{Keywords: Robot Path Planning, Soft Predicates, Resolution-Exact Algorithm, Subdivision Search}
}
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