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Testing of instruments. All new models of universal 
stereoplotters are tested according to a uniform program. 
The test program has been elaborated with due regard to 
technical performance, field of application and econo- 
mical efficiency of the new instruments. 
Áccuracy of instruments is estimated by measuring 
a grid model (control grids) and photographic models 
corresponding to vertical survey (c = @ = 2910) of 
an accidental country ( baux * hain = 600 m ). 
Sometimes, accuracy of the stereoplotters is estimated 
on the base of standard tests, as are recommended by ISP 
and executed in two steps: | 
1) Monocular testing of individual projectors of the 
instrument; 
2) General stereoscopic examination of the instrument 
as a whole. 
COMMISSION III. 
  
Aerotriangulation. 
  
Photogrammetric control extension needed for making 
topographical maps by stereophotogrammetric methods is 
established with the help of spatial photogrammetric 
networks plotted either on analog instruments or by 
analytical means. 
As a chief coordinate recorder, the ZeiB Stereo- 
comparator 18 x 18 cm is used. 
In establishing both the algorithm and program 
for an electronic computer,great attention is being 
paid to intermediate control operations with the aim of 
revealing errors ( erroneous data ) in the process of 
calculation and to eliminate these from further 
computations. 
However, the method of checking the work and eliminat- 
ing errors at control points has not as yet been suffi- 
ciently well elaborated, especially in the cases where 
there are only a few control pointse 
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