You may remember Dali worked with anamorphic images that were recreated on a glossy surface of a metal tube (also the huge one sculpture in Figueres city featuring Dali's face). As for Salvador Dali he did pictures and all mathematics by himself, as for modern figurative sculptor Jonty Hurwitz, computing is a first thing before he begins to create complex anamorphic sculptures. That's clear the process cannot rely only on hands and an eye. http://www.youtube.com/watch?feature=player_embedded&v=W3SIEt37FjI

For the anamorphic pieces its an algorithmic thing, distorting the original sculptures in 3D space using 2πr or πr3 (cubed). Much of it is mathematical, relying on processing power. There is also a lot of hand manipulation to make it all work properly too as spacial transformation have a subtle sweet spot which can only be found by eye. Generally I will 3D scan my subject in a lab and then work the model using Mathematica or a range of 3D software tools. I think the π factor is really important in these pieces. We all know about this irrational number but the anamorphic pieces really are a distortion of a “normal” sculpture onto an imaginary sphere with its centre at the heart of the cylinder.

http://www.youtube.com/watch?v=Z3hAojDjNhA&feature=player_embedded&list=UUsJTahxI36FEd4dKjOdZdpQ