Gnomon
A painted stick dating from 2300 BC that was excavated at the archeological site of Taosi is the oldest gnomon known in China.
[4] The gnomon was widely used in ancient China from the second millennium BC onward in order to determine the changes in seasons, orientation, and geographical latitude.
[citation needed] Vitruvius mentions the gnomon as "gnonomice" in the first sentence of chapter 3 in volume 1 of his book De Architectura.
Despite its similarity to "γνωμονικός" (or its feminine form "γνωμονική"), it appears unlikely that Vitruvius refers to judgement on the one hand or to the design of sundials on the other.
[citation needed] Perforated gnomons projecting a pinhole image of the Sun whose location can be measured to tell the time of day and year were described in the Chinese Zhoubi Suanjing, possibly dating as early as the early Zhou (11th century BC) but surviving only in forms dating to the Eastern Han (3rd century).
[11] In the Northern Hemisphere, the shadow-casting edge of a sundial gnomon is normally oriented so that it points due northward and is parallel to the rotational axis of Earth.
While the rod's shadow indicated the direction of the Sun, the grayscale paints of varying reflectivity and the red, green and blue patches facilitated proper photography on the surface on the Moon.
A three-dimensional gnomon is commonly used in CAD and computer graphics as an aid to positioning objects in the virtual world.
