E DLKOTE s 1T 
PPO OGRANMPILIKY, Vol. AZEA 
i 
  
Communication to 
VIII International Congress for Photogrammetry 
Reprint from 
Svensk Lantmateritidskrift 
Congress Number 1956 
Commission 11 
DEVICE FOR MEASUREMENTS OF PARALLAXES 
By 
Gunnar Simonsson 
The devices usually used for parallax measurements by means of 
mirror or pocket stereoscopes in aerial photographs are: Stereometers 
(or parallax bars) and parallax wedges. 
The stereometer is a micrometer screw to which are attached two 
glass plates carrying the measuring marks. By screwing the micrometer 
the two marks can be set to identical details in the two photographs, the 
distance between these details — the horizontal parallax — being read 
on a reading drum. 
The parallax wedge consists of two non — parallel lines engraved on 
the bottom of a glass plate. Corresponding parts of the lines are brought 
to coinside with identical details in the photographs. The horizontal pa- 
rallaxes can be read on a scale close to one (or both) of the lines. 
Fundamentally the device here described is a type of parallax wedge, 
the lines being substituted by rows of dots. The rows, instead of being 
straight lines, form the systems of points shown by Figure 1. As the 
two lines of the wedge are not parallel, consequently, the two point sys- 
tems in Figure 1 have to be unequally shaped. The point row starts with 
the first point in the U-shaped point group at the top of the system, 
(See Figure 4), follows the sequences of point groups, and ends with 
the last point in the point group at the bottom of the system. Each point 
in the left system corresponds to a point in the right system. A point 
step represents a parallax difference of 1/10 millimeter. Thus each 
point group represents a parallax difference of 1 millimeter and, con- 
sequently, the whole system, consisting of 20 point groups, allows mea- 
suring parallax differences up to 20 millimeters. s 
There are two obvious advantages of this arrangement of the points: 
l. All points required for the parallax measurements are concentrated 
Within a small area, which means that the plate can be attached to the 
Stereoscope at the beginning of the work and need not then be remo- 
ved. (Only small adjustment of vertical parallaxes may be needed.) 
  
  
  
  
  
    
    
       
   
  
  
   
  
  
  
   
    
   
  
  
  
  
   
  
   
   
  
  
  
  
    
  
   
   
   
  
  
     
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