Shadows : Posts
Figure 1a and 1b: Shadow produced by the post AB by a light-source S : Create T as crossing-point of HL with a perpendicular line to HL through S. Draw line through S and B, and through T and A to create V: AV presents the shadow p of the post AB.
Figure 1c :The extension-lines through VW, AC and BD meet in Z. The lines ZV and BZ define a plane with a Vanishing Line (VL) through S and VP.
Figure 2a and 2b : Creation of the shadow of post AB given the shadow q of post CD : Create T as crossing-point of the prolongation of q and HL, create S as crossing point of the vertical through T with a line through W and D. Create V as crossing-points of the lines through S and B and T and A.
Figure 2c analog to figure 1c
Figure 3a and 3b : Position of the light-source behind of the observer.