COMPENSATION FOR VERTICAL EXAGGERATION 
When two vertical aerial photographs are viewed stereoscopically, vertical 
exaggeration is generally present (fig. 5b). This vertical exaggeration causes alti- 
tudes to appear higher than they are, in reference to the horizontal scale of the 
Therefore, all angles of slope appear steeper than they actually 
are. This vertical exaggeration can be expressed as the ratio of the vertical scale to 
the horizontal scale and is called the Exaggeration Factor. In considering only angles 
of slope, the Exaggeration Factor may be expressed by the following formula: 
stereoscopic model. 
Tangent of exaggerated angle of slope 
Tangent of true angle of slope 
Exaggeration Factor = 
Five factors that affect vertical exaggeration are: 
|. The focal length of the camera taking the pictures. 
2. The photo base of the stereoscopic pair of photographs. 
3. The image separation of the photographs under the stereoscope. 
4. The eye base of the person viewing the pictures. 
5. The viewing distance. (The distance the image rays travel 
from the photographs to the viewer's eyes.) 
ns of the Stereo-slope Comparator and 
In determining angles of slope by mea 
ors of vertical exaggeration are compen= 
the Supplementary Slope Model , these five fact 
sated in the following manner. 
Focal length and photo base. == The effect of focal length and photo base 
on the amount of vertical exaggeration Is compensated in the computed true angles of 
slope shown in the table on the right-hand side of the Supplementary Slope Model . 
Image separation. == By maintaining the same separation of images when 
measuring the ve of slope of the Supplementary Slope Model and angles of slope on 
the stereoscopic model from the aerial photographs, the effect of image separation on 
vertical exaggeration remains constant and can be disregarded. 
Eye base and viewing distance. -- The eye base of an individual is a constant 
distance. The viewing distance of any one stereoscope at a fixed magnification is also 
a constant factor. Any vertical exaggeration caused by these factors is believed to 
equally affect the stereoscopic target of the Stereo-slope Comparator, the Supplementary 
Slope Model , and the stereoscopic photo model. In connection with the method of slope 
bed in this paper these factors can thus be disregarded. 
measurement descri 
I3