Exact algorithms for terrain guarding

Pradeesha Ashok, Fedor V. Fomin, Sudeshna Kolay, Saket Saurabh, Meirav Zehavi

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Scopus citations


Given a 1.5-dimensional terrain T, also known as an x-monotone polygonal chain, the TERRAIN GUARDING problem seeks a set of points of minimum size on T that guards all of the points on T. Here, we say that a point p guards a point q if no point of the line segment pq is strictly below T. The TERRAIN GUARDING problem has been extensively studied for over 20 years. In 2005 it was already established that this problem admits a constant-factor approximation algorithm [SODA 2005]. However, only in 2010 King and Krohn [SODA 2010] finally showed that TERRAIN GUARDING is NP-hard. In spite of the remarkable developments in approximation algorithms for TERRAIN GUARDING, next to nothing is known about its parameterized complexity. In particular, the most intriguing open questions in this direction ask whether it admits a subexponential-time algorithm and whether it is fixed-parameter tractable. In this paper, we answer the first question affirmatively by developing an nO(√k)-time algorithm for both DISCRETE TERRAIN GUARDING and CONTINUOUS TERRAIN GUARDING. We also make non-trivial progress with respect to the second question: we show that DISCRETE ORTHOGONAL TERRAIN GUARDING, a well-studied special case of TERRAIN GUARDING, is fixed-parameter tractable.

Original languageEnglish
Title of host publication33rd International Symposium on Computational Geometry, SoCG 2017
EditorsMatthew J. Katz, Boris Aronov
PublisherSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
Number of pages1005
ISBN (Electronic)9783959770385
StatePublished - 1 Jun 2017
Externally publishedYes
Event33rd International Symposium on Computational Geometry, SoCG 2017 - Brisbane, Australia
Duration: 4 Jul 20177 Jul 2017

Publication series

NameLeibniz International Proceedings in Informatics, LIPIcs
ISSN (Print)1868-8969


Conference33rd International Symposium on Computational Geometry, SoCG 2017


  • Art Gallery
  • Exponential-time algorithms
  • Terrain guarding


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