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