(472) 
The aim of this report is therefore to describe a method of distance trian- 
gulation in air photographs which works under the same conditions as radial 
triangulation. This method makes necessary small tilts and small differences in 
height. 
The basic idea is marked by the fact that in every vertical photograph 
there are distances which are reflected in the photograph in the same scale in 
spite of nadir distance. Among the many distances which respond to these con- 
ditions there is also a particularly characteristic pair of distances, the socalled 
“T”-figure. If two distances s’ and q’ form a T-figure in the photograph, both 
lines of T-figure are distances which show the same scale in the photograph. 
The only restricting condition is the requisition that the foot of the T coincides 
by and large with the principal point. If there are two vertical photographs 
which overlap lightly the T-figures may be used to determine the picture scale 
of a distance s» in the second photograph, if the picture scale of another 
distance s; in the first photograph is known. This is explained in the following 
example: 
The respective equations 
  
  
  
  
  
  
  
are: 
S S1 s so’ 
31 1 2 52 
SET and ee > ! 
qi qu 2 q2 82 
As qi! and q»' are pictures 
of the same ground distance, / 
we find: 72 
/ / 
$2.1 
sp >. 
Sı .Q2 
Thus distance sa is deduced by triangulation from distance sı. 
Considering a sequence of air photographs which are overlapping more 
than 50% the distances of air polygon may be determined by means of T- 
figures. À sequence of 5 air photographs serves as example: 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
4, 323 522; 3% ag 354 
/ , / / + 
^e 5 532. si fos $5 
/ / / 7 7 / 
S 32.S43.S 54 G 12 - G 23 . Q 34 
S4 == Ze TA tn / / r^ / $1 
S12.S23.S 34 G 32 . G 43 . G 54 
As in each case the distances s' and q' do not differ strongly among them- 
selves the method can be applied for measurement of distance parallaxes in the 
photographs. The respective formula is: 
The distance parallaxes can be measured stereoscopically and therefore 
very accurately by a parallax micrometer screw. The tentative scale is hereby