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where c is a constant. In this solution, the orthophoto is 
an orthogonal projection of the stereomodel on a reference 
plane, whereas the stereomate is an oblique projection of 
the stereo-model on the same reference plane. This is il- 
lustrated schematically in the figure below. 
  
  
  
  
  
KY + 
be P| 
  
Fig.17 Basic geometry of stereo-orthophotos. 
In reality, there is a slight deviation from this 
very simple geometry but for the purpose of our present 
discussion the above definition is acceptable and suffi- 
cient. 
It is important to note, that in this type of 
stereopair the vertical parallaxes at corresponding 
Points have been removed. As a result, the stereo-view- 
ing of the pair, using any magnification in the viewing 
system, is extremely simple and can be achieved by means 
of a stereoscope. The observed model, as compared to a 
single orthophoto, has obviously superior definition, 
is metrically correct, and.the heights of the terrain 
points and the "elevated" features can be measured. 
Thus, by substituting stereo-orthophotos for the 
original aerial photographs a very flexible and self- 
contained mapping and photointerpretation system of ex- 
treme simplicity has been created. 
The author developed the two instruments that con- 
stitute the system. 
- "Orthocartograph", an instrument for product- 
ion of stereo-orthophotos in one single 
operation. 
- "Stereocompiler", a simple instrument for pro- 
cessing of stereo-orthophotos (graphical plot- 
ting and numerical determination of coordinates)