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Bounded Voronoi Tesselation using the algorithm described in xlr8r.info and an alpha shape

This is a variant of the Bounded Voronoi Tessellation, with:

sites distributed around two poles

poles are indentified with an alpha-shape (we then use the convex hull of each pole) - thanks to Jason Davies for the `boundary()`

function (aka `polygonBoundary`

)

the median distance instead of the mean (allowing a small optimisation)

many more exterior control points

a d3.curveCatmullRomClosed convex hull shape

not displaying links and sites

Author: Philippe Rivière, August 2016

Based on mbostock‘s block: Voronoi Tessellation

forked from Fil‘s block: Circular Bounded Voronoi Tessellation