de 
one photographic image and by following the previously 
recorded profiles. Today, we could classify his procedure 
as an "off. line” or. "storage: mode! approach, 
  
Fig.l... The. Ferber~Galus plotter 
Ferber also very correctly recognized the import- 
ance of and argued for the use of his "planes photogra- 
phies". . Many. of his: arguments.one can find in recent 
publications, which is the best proof of the imaginative 
quality of his effort. .Reading his original work after a 
lapse of so many years is most refreshing and gives an 
exciting insight into the mechanics of some photogramme- 
tric developments. 
At about the same time, O. Lacmann in Germany 
developed a special differential rectifier described very 
briefly in his publication [2] of 1931, He followed es- 
sentially. the same: principle as Ferber. . In the product- 
jon process, a knowledge of the terrain or of its profiles 
was assumed. The projection distance of any given image 
  
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