# How does sorting come into play with convex hull?

I am investigating a convex hull algorithm that involves sorting. In fact, its running time is limited by sorting, so it is $O(n \log n)$, where $n$ is the number of points on the plane.

That algorithm first sorts the points by x-coordinates. It then includes the first and last points in the convex hull. From there on, I am confused. How could an algorithm like this get the other points of the hull?

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Which algorithm are you looking at? There are several that involve sorting (q.v. Convex Hull Algorithms on Wikipedia). –  Luke Mathieson Nov 30 '12 at 7:56
He is most likely talking about the incremental algorithm for the convex hull. What I do not understand is what exactly is your misunderstanding, David? –  Jernej Nov 30 '12 at 9:42