Plane and Stereographic Projections of Convex Polyhedra from Minimal Information

Many programs have been written, usually for engineering purposes, to draw plane, trimetric, isometric and stereographic projections of frameworks which are not necessarily convex. The word framework here is used to imply that the technique is not used to draw solid bodies in the sense that only those edges which are visible from the given viewpoint are drawn. The technique used is to specify, in addition to the viewpoint and centre of vision, both the space coordinates of the vertices and the way in which they are joined in pairs to form the rods of the framework. The vertices are then projected into a plane perpendicular to the line joining the viewpoint to the centre of vision by the method briefly described in the next section or by some similar method. The virtue of a particular program can then be judged by the efficiency with which the edges are drawn by the plotter. The resulting diagram is meaningful to a draughtsman but is frequently of little meaning to other viewers.