A Topological Picture Book, Rendered

Plate I. The torus. A Topological Picture Book controls Hand-hatched surfaces after the mid-century manner of Francis, Apéry, Hilbert–Cohn-Vossen. Drag to turn the model freely (shift-drag to roll it); scroll to approach. On a touch screen, one finger turns, two fingers pinch to approach and twist to roll. Surface parametric implicit Preset x(u,v) y(u,v) z(u,v) u from / to v from / to u segments v segments trace the double curve (self-intersection) f(x,y,z) = 0 box half-width grid r