1. A computer drawing system, comprising: a two dimensional input device; a display device; a processor connected to the input device and the display device, wherein the processor includes memory containing computer readable instructions which, when executed, cause the processor to: define a three dimensional shape model; receive from the two dimensional input devices an input indicative of a two dimensional hand drawn element; map the two dimensional hand drawn element to a corresponding portion of the three dimensional shape model; and modify the corresponding portion of the three dimensional shape model to resemble the two dimensional hand drawn element.