Abstract
We study the problem of finding shortest tours/paths for “lawn mowing” and “milling” problems: Given a region
in the plane, and given the shape of a “cutter” (typically, a circle or a square), find a shortest tour/path for the cutter
such that every point within the region is covered by the cutter at some position along the tour/path. In the milling
version of the problem, the cutter is constrained to stay within the region. The milling problem arises naturally in
the area of automatic tool path generation for NC pocket machining. The lawn mowing problem arises in optical
inspection, spray painting, and optimal search planning.
Both problems are NP-hard in general. We give efficient constant-factor approximation algorithms for both
problems. In particular, we give a .3 C "/-approximation algorithm for the lawn mowing problem and a 2.5-
approximation algorithm for the milling problem. Furthermore, we give a simple 65
-approximation algorithm for
the TSP problem in simple grid graphs, which leads to an 11
5 -approximation algorithmfor milling simple rectilinear
polygons. Ó 2000 Elsevier Science B.V. All rights reserved.
Keywords: Computational geometry; Geometric optimization; Approximation algorithms; NP-completeness;
Traveling salesman problem (TSP); Lawn mowing; Milling; NC machining
AbstractWe study the problem of finding shortest tours/paths for “lawn mowing” and “milling” problems: Given a regionin the plane, and given the shape of a “cutter” (typically, a circle or a square), find a shortest tour/path for the cuttersuch that every point within the region is covered by the cutter at some position along the tour/path. In the millingversion of the problem, the cutter is constrained to stay within the region. The milling problem arises naturally inthe area of automatic tool path generation for NC pocket machining. The lawn mowing problem arises in opticalinspection, spray painting, and optimal search planning.Both problems are NP-hard in general. We give efficient constant-factor approximation algorithms for bothproblems. In particular, we give a .3 C "/-approximation algorithm for the lawn mowing problem and a 2.5-approximation algorithm for the milling problem. Furthermore, we give a simple 65-approximation algorithm forthe TSP problem in simple grid graphs, which leads to an 115 -approximation algorithmfor milling simple rectilinearpolygons. Ó 2000 Elsevier Science B.V. All rights reserved.Keywords: Computational geometry; Geometric optimization; Approximation algorithms; NP-completeness;Traveling salesman problem (TSP); Lawn mowing; Milling; NC machining
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