4.5 Vertical Exaggeration

Vertical exaggeration is present in all stereo pairs. It exists because of disparity between the vertical and horizontal scales of a stereomodel. Under normal conditions, the vertical scale will appear greater than the horizontal. Image interpreters must take this effect into consideration when estimating heights of objects and rates of slopes.

Vertical exaggeration is best understood by considering the relationship between the imaging geometry and the viewing geometry of a stereo model.

Vertical Exaggeration - Imaging Geometry

• B_n = air (imaging) base
• H_n = imaging height
• W_n = width of target
• p_n = parallax of point "A" due to elevation h_n
• h_n = target height

Vertical Exaggeration - Viewing Geometry

• B_s = stereo viewing base
• H_s = stereo viewing height
• W_s = apparent width of target
• h_s = apparent height of "A"
• p_s = apparent parallax of point "A"
• p_i /2 = one half of p_sas measured in one image
• w_i /2 = one half of w_sas measured in one image

Vertical exaggeration is the difference between the imaging base to height (B_n/H_n) and the stereo-viewing base to height (B_s/H_s) ratios. B_n/H_n is the ratio of the air base (distance between the two exposure stations) to the flight altitude above average ground. B_s/H_s is the ratio of the eye base to the distance from the eyes at which the stereo-model is viewed.