A First Algorithm: Planar Convex Hulls

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چکیده

We will start with a simple geometric problem, the computation of the convex hull of a finite set of points in the plane. We will formulate a basic algorithm that constructs the planar hull in quadratic time. It accesses the input points through a single predicate, the orientation predicate for three points. We will see how this predicate can be realized by a simple formula in the point coordinates. Next we discuss two techniques for improving the running time to O(n log n), where n is the number of input points. Collinear points require special care in convex hull algorithms and hence we call them a degeneracy. Finally, the algorithm would lead directly to an implementation if we had a Real-RAM to our disposal.

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تاریخ انتشار 2009