Hierarchical vertical decompositions, ray shooting, and circular arc queries in simple polygons

Abstract

A new hierarchical decomposition of a simple polygon is introduced. The hierarchy has depth O(log n), linear size, and its regions have maximum degree three. Using this hierarchy, circular ray shooting queries in a simple polygon can be answered in O(log* n) query time and O(nlogn) space. If the radius of the circle is fixed, the query time can be improved to O(logn) and the space to O(n). The decomposition is also applied to three other circular arc query problems: shortest directed arc, arc bending, and arc pushing. Using these queries, the largest empty lune determined by two query points in a simple polygon can be computed in O(log3 n) time, while the circular visibility region of a query point in a simple polygon can be reported in time O(m log3 n), where m is the output size.