Well ... This is what I undestood :

1) Sort each point by X ascending
2) for each point, make a triangle with the point n, point n +1, point n+2 then calculate the barycentre of this triangle. So if other points are ouside the circle of center=barycentre and distance=barycentre to any edge of triangle then you're alowed to use this triangle.

It's more or less delaunay algorithm which is dual to voronoi

I still don't understand how to draw voronoi diagram.

Do someone has any documents on how-to contruct it ?