In nice drawing Fatin Uluengin shows the transition of a 2D plan to a 3D realisation.[br]From bottom to the top:[br][list][*]Upon the 2D plan cells are placed whose ground plane matches with the figures of the plan.[/*][*]These cellen form concentric circles.[/*][*]In 3D one puts these concentric circles one upon the other.[/*][/list]

Next applet shows dynamicly this transition from a plan to a 3D construction.