The Grid in Positive Position 
O Control Points 
  
Points for Determination of the Radial Distortion 
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According to the grid method [1] the radial distortion in 
plane is defined as 
where r = 
h = the length of the perpendicular from the projection 
centre to the projection plane 
dz, — the translation of the projection centre in the z — direc- 
tion 
dz, is determined after adjustment according to the method of the 
least squares of the errors of the measured coordinates in points at the 
same radial distance from the centre. 
The projectors of a plotting instrument are investigated one by one. 
Projected or photographed grid coordinates are measured at a prelimi- 
narily determined enlargement. The grid- and projection planes are 
the radial distance from the centre 
      
  
  
  
  
  
  
  
  
  
  
  
  
   
   
   
   
  
    
the grid 
(1)