A watchman tour in a polygonal domain (for short, polygon) is a closed curve such that every point in the polygon is visible from at least one point of the tour. The problem of finding a shortest watchman tour is NPhard for polygons with holes. We show that the length of a minimum watchman tour in a polygon P with k holes is O(per(P) + k
Adrian Dumitrescu, Csaba D. Tóth