On finding an empty staircase polygon of largest area (width) in a planar point-set

  • Authors:
  • Subhas C. Nandy;Bhargab B. Bhattacharya

  • Affiliations:
  • Advanced Computing and Micro-electronics Unit, Indian Statistical Institute, 203 B.T. Road, Calcutta 700 108, India;Advanced Computing and Micro-electronics Unit, Indian Statistical Institute, 203 B.T. Road, Calcutta 700 108, India

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

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Abstract

This paper presents an algorithm for identifying a maximal empty-staircase-polygon (MESP) of largest area, among a set of n points on a rectangular floor. A staircase polygon is an isothetic polygon bounded by two monotonically rising (falling) staircases. A monotonically rising staircase is a sequence of alternatingly horizontal and vertical line segments from the bottom-left corner of the floor to its top-right corner such that for every pair of points α = (xα, yα) and β = (xβ, yβ) on the staircase, xα ≤ xβ implies yα ≤ yβ. A monotonically falling staircase can similarly be defined from the bottom-right corner of the floor to its top-left corner. An empty staircase polygon is a MESP if it is not contained in another larger empty staircase polygon. The problem of recognizing the largest MESP is formulated using permutation graph, and a simple O(n3) time algorithm is proposed. Next, based on certain novel geometric properties of the problem, an improved algorithm is developed that identifies the largest MESP in O(n2) time and space. The algorithm can be easily tailored for identifying the widest MESP in a similar environment. The general problem of locating the largest area/width MESP among a set of isothetic polygonal obstacles, can be solved easily. These geometric optimization problems have several applications to VLSI layout design, robot motion planning, to name a few.