Silhouette from given point.

(animated .gif > view full size)
Again playing with derivative graph...
Heavy definition.
Colliding a plane with the 3d-derivative-graph to get silhouette curves.
(or more specific, curves constructed over points where surface normals are normals to rays directed to main point.. What?!)
This is a scenario where I've extracted only the "front" part of the curves,(by trimming the curves where them are also tangent with local rays), giving as output only the silhouette;
and then used those curves to "cast" a possible "shadow", for a illuminated/not-illuminated area study stuff or such...
Math is fun! :D