Chapter notes

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## Chapter notes

This chapter barely scratches the surface of computational-geometry algorithms and techniques. Books on computational geometry include those by Preparata and Shamos [247], Edelsbrunner [83], and O'Rourke [235].

Although geometry has been studied since antiquity, the development of algorithms for geometric problems is relatively new. Preparata and Shamos note that the earliest notion of the complexity of a problem was given by E. Lemoine in 1902. He was studying euclidean constructions-those using a compass and a ruler-and devised a set of five primitives: placing one leg of the compass on a given point, placing one leg of the compass on a given line, drawing a circle, passing the ruler's edge through a given point, and drawing a line. Lemoine was interested in the number of primitives needed to effect a given construction; he called this amount the "simplicity" of the construction.

The algorithm of Section 33.2, which determines whether any segments intersect, is due to Shamos and Hoey [275].

The original version of Graham's scan is given by Graham [130]. The package-wrapping algorithm is due to Jarvis [165]. Using a decision-tree model of computation, Yao [318] proved a lower bound of Ω(n lg n) for the running time of any convex-hull algorithm. When the number of vertices h of the convex hull is taken into account, the prune-and-search algorithm of Kirkpatrick and Seidel [180], which takes O(n lg h) time, is asymptotically optimal.

The O(n lg n)-time divide-and-conquer algorithm for finding the closest pair of points is by Shamos and appears in Preparata and Shamos [247]. Preparata and Shamos also show that the algorithm is asymptotically optimal in a decision-tree model.

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