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1 
1 
Fig. 2. The general distribution of topography- 
factors in Sweden. Factor 2 means for example 
that the maximum elevation difference within an 
arbitrarely chosen 5 X 5-km-area is 200 metres. 
errors in the principal point about ten times the abovementioned. This 
can of course not be disregarded but must not be discouraging as 
1:0 such maximum nadir distances occur very seldom 
2:0 they can easily be established, e. g. with a simple parallax-inspec- 
tion on light table, and than the direction angles can be corrected 
3:0 modern gyro-methods for camera-stabilizing or for registration 
of tip and tilt completely eliminate this "problem". 
The height-differences in the terrain, or, as a matter of fact, the in- 
clinations of the lines in the terrain from the terrainpoint corresponding 
to the principal point to the terrairi-points corresponding to the radial 
points, introduce errors in the direction angles when the nadir distance 
is not zero. The human eye and mind, howewer, overestimate this in- 
clination 2 to 3 times. The author's statistical investigations, based on 
Swedish and foreign contour maps, show 1:0 that this inclination (tg8) 
is proportional to the topography factor (T = greatest height differen- 
ces in decameter within a 5 X 5 km-square) 
  
  
  
  
  
  
d REEL EIER | EL p E EE 
EE Cu RE E E EE 
    
me ee Nt 
CRE ne RES 
  
  
  
  
    
    
p RE 
     
  
  
   
      
  
  
   
  
   
  
  
  
  
  
  
  
  
  
  
   
  
  
dpt etre