Two towels on a beach—an application of Desargues's theorem
This scene shows two towels of the same shape spread out on a beach. You can change the shape of the red towel (which changes the shape of the blue towel), you can change the locations of the blue and red towels, and you can change the locations of the two vanishing points. To view this scene correctly place your eye at the same height as the horizon on the semicircle with the vanishing points as endpoints. Check the checkbox to see the lines used to draw the figures.