1. A drawing system, comprising: a computer system having a display and a pen input device having a pen stylus; the computer system having curve model generation software running thereon; the curve model generation software responsive to one or more strokes of made with the pen stylus to sketch a first 2D curve and generating a first 2D vector curve therefrom; the curve model generation software displaying a guide on the display to guide the user in sketching a second curve; the curve model generation software responsive to one or more strokes made by the user with the pen stylus to sketch a second 2D curve and generating a second 2D vector curve therefrom; and the curve model generation software generating a pair of mirror symmetric 3D vector curves from the first and second 2D vector curves which are displayed on a canvas displayed on the display; wherein the generation of the pair of the mirror symmetric 3D curves by the curve model generation software generates the pair of mirror symmetric 3D includes the curve model generation software: calculating 3D curve c 1 on the display from the first 2D vector curve; creating a ray surface R starting from an eye position e and containing c 1 ; creating a mirrored ray surface R M of R where R M starts from a mirrored eye position e M ; displaying R M on the display where R M converges to a vanishing point and provides the guide for the sketching of the second 2D curve; calculating a second 3D curve c 2 from the second 2D vector curve; creating a 3D curve C 2 by projecting C 2 onto R M ; and creating 3D curve C 1 by mirroring C 2 where 3D curves C 1 and C 2 are the pair of mirror symmetric 3D curves.