Optics principles. For example, the Ames room, Hering, Müller-Lyer, Orbison, Ponzo, Sander, and Wundt illusions all rely on the suggestion of the appearance of distance by using converging and diverging lines, in the same way that parallel light rays (or indeed any set of parallel lines) appear to converge at a vanishing point at infinity in two-dimensionally rendered images with artistic perspective. This suggestion is also responsible for the famous moon illusion where the moon, despite having essentially the same angular size, appears much larger near the horizon than it does at zenith. This illusion so confounded Ptolemy that he incorrectly
Distance from a point to a line length of this projection is given by: Now, thus Since "Q" is a point on the line, formula_27, and so, It is possible to produce another expression to find the shortest distance of a point to a line. This derivation also requires that the line is not vertical or horizontal. The point P is given with coordinates (formula_29). The equation of a line is given by formula_30. The equation of the normal of that line which passes through the point P is given formula_31. The point at which these two lines intersect is the closest point on the original line