The mathematics of sidewalk illusions

Have you ever come across an oddly stretched image on the sidewalk, only to find that it looks remarkably realistic if you stand in exactly the right spot? These sidewalk illusions employ a technique called anamorphosis — a special case of perspective art where artists represent 3D views on 2D surfaces. So how is it done? Fumiko Futamura traces the history and mathematics of perspective.
Read more: http://snapzu.com/gladsdotter/the-mathematics-of-sidewalk-illusions?source=Snapzu