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Several enclosing circles are possible for a given set of N 2D points. I am only talking about enclosing circles having 3 or more points on the circumference. What is the asymptotic limit of the total number of distinct enclosing circles having 3 or more points on the circumference. The naive bound is $O(n^3)$ but tighter bound should exist.

And also how to generate all such enclosing circles?

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An enclosing circle (by your definition) corresponds to a triangular face of the farthest point Delaunay triangulation, which is a triangulation of the convex hull of the input. For points in general position it always has exactly $h-2$ faces where $h$ is the number of convex hull vertices. Therefore the number of enclosing circles is also $h-2$.

They can be generated by constructing the farthest point Delaunay triangulation, in $O(n\log n)$ time.

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