The Square-grid concept h/d
Images 1-4 present a virtual cube (marks of heights are fixed on trees) pictured from close, 7.5, 10 and 15 meters.
Figure 1 shows a graphical presentation of the calculated result v/w = h/d based on the scheme and formulas presented below in form of a grid.
Figure 2 is identical to figure 1 except that instead of the central red square, a blue square is presented adjectant to the vertical to the Horizontal Line (HL) through the Vanishing Point (VP).
Note that the red square in figure 1 is of equal size than the blue square in figure 2 and that both squares exhibit the same ratio of v/w.
The term h/d allows to estimate the ratio of the visually perceived heights v and the visually perceived length w of a square at a given distance d from the Stand Point (SP), at a heights h of the position of the eyes over ground. (Valid for h/d smaller than 0.3, thus e.g. for an eye-position of 1.5 m over ground and an object not closer than 5 m to the Stand Point (SP)).