Half-Guarding Weakly-Visible Polygons and Terrains

Authors Nandhana Duraisamy, Hannah Miller Hillberg, Ramesh K. Jallu , Erik Krohn , Anil Maheshwari, Subhas C. Nandy, Alex Pahlow

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Author Details

Nandhana Duraisamy
  • PSG College of Technology, Coimbatore, India
Hannah Miller Hillberg
  • University of Wisconsin, Oshkosh, WI, USA
Ramesh K. Jallu
  • Indian Institute of Information Technology Raichur, India
Erik Krohn
  • University of Wisconsin, Oshkosh, WI, USA
Anil Maheshwari
  • Carleton University, Ottawa, Canada
Subhas C. Nandy
  • Indian Statistical Institute, Kolkata, India
Alex Pahlow
  • University of Wisconsin, Oshkosh, WI, USA

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Nandhana Duraisamy, Hannah Miller Hillberg, Ramesh K. Jallu, Erik Krohn, Anil Maheshwari, Subhas C. Nandy, and Alex Pahlow. Half-Guarding Weakly-Visible Polygons and Terrains. In 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 250, pp. 18:1-18:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


We consider a variant of the art gallery problem where all guards are limited to seeing 180degree. Guards that can only see in one direction are called half-guards. We give a polynomial time approximation scheme for vertex guarding the vertices of a weakly-visible polygon with half-guards. We extend this to vertex guarding the boundary of a weakly-visible polygon with half-guards. We also show NP-hardness for vertex guarding a weakly-visible polygon with half-guards. Lastly, we show that the orientation of half-guards is critical in terrain guarding. Depending on the orientation of the half-guards, the problem is either very easy (polynomial time solvable) or very hard (NP-hard).

Subject Classification

ACM Subject Classification
  • Theory of computation → Approximation algorithms analysis
  • Art Gallery Problem
  • Approximation Algorithm
  • NP-Hardness
  • Monotone Polygons
  • Half-Guards


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