Perspective foreshortening is caused by the way the human eye perceives the world due to its physical structure (for example, excitation of cone cells in the retina), and to the optical geometry of light rays (due to the nature of light itself).
As objects become more distant, they appear smaller because their visual angle decreases. The eye is at the vertex of a triangle with the object at its base, so the greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle (Euclidean geometry).
|Canopied footway in perspective|
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