2.2. Data Reduction 
2.2.1. The Analogue Approach 
In this approach, almost any of the commercially available 
stereoplotters could be used. Because of the rather short prin- 
cipal distance in stereometric cameras, and the limited range 
of principal distances to be used in stereoplotters, one generally 
has to resort to an affine stereo model, unless one of the few 
specially constructed stereoplotters is used. Among the stereo- 
plotters specifically adapted to the stereometric camera condi- 
tions are: ZEISS Terragraph (Fig.9) and WILD A-40 (Fig. 10). 
Such specialized plotters are more convenient to use for stereo- 
metric camera photography, but are generally restricted to the 
"normal case'' of photogrammetry. 
Fig. 9 - ZEISS Terragraph Fig. 10 - WILD A-40 
2.2.2 The Analytical Approach 
  
In this approach, instrumental operations are reduced to 
the simple measurement of plate coordinates. Such measure-