Art gallery theorems for guarded guards

  • Authors:
  • T. S. Michael;Val Pinciu

  • Affiliations:
  • Mathematics Department, United States Naval Academy, Annapolis, MD;Mathematics Department, Southern Connecticut State University, New Haven, CT

  • Venue:
  • Computational Geometry: Theory and Applications
  • Year:
  • 2003

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Abstract

We prove two art gallery theorems in which the guards must guard one another in addition to the gallery. A set G of points (the guards) in a simple closed polygon (the art gallery) is a guarded guard set provided (i) every point in the polygon is visible to some point in G; and (ii) every point in G is visible to some other point in G. We prove that a polygon with n sides always has a guarded guard set of cardinality ⌊(3n - 1)/7⌋ and that this bound is sharp (n ≥ 5); our result corrects an erroneous formula in the literature. We also use a coloring argument to give an entirely new proof that the corresponding sharp function for orthogonal polygons is ⌊n/3⌋ for n ≥ 6; this result was originally established by induction by Hernández-Peñalver.