A sliding camera travelling along a line segment s in a polygon P can see a point p in P if and only if p lies on a line segment contained in P that intersects s at a right angle. The objective of the minimum sliding cameras (MSC) problem is to guard P with the fewest sliding cameras possible, each of which is a horizontal or vertical line segment. In this paper, we give an O(n~03)-time 3-approximation algorithm for the MSC problem on any simple orthogonal polygon with n vertices. Our algorithm involves establishing a connection between the MSC problem and the problem of guarding simple grids with periscope guards.
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