| +95 +55 +15 
  
  
  
  
  
  
Fig. 4. Mask with slots to be placed in the left projector for y-parallax measurements in models over rugged ground. 
Point 15 is assumed to coincide with the principal point. 
If the y-parallaxes are to be measured in ordinary plotting instruments, the point scheme (Fig. 3) 
can be constructed upon the drawing board after plotting points 15 and 95 from the model. The 
model points are then found from adjusting the drawing pen (microscope) over the corresponding 
points on the drawing board. For the measurements of y-parallaxes with mirror stereoscope and 
parallax bar the construction can be made in a contact print. In this case comparatively small eleva- 
tion differences on the ground and small inclinations of the photographs must be required. (The 
elevation differences on the ground should preferably not exceed 10— 15 9j of the flying altitude and 
the inclinations o and c should not exceed 1*— 175.) 
In general it is important that the y-parallaxes shall be measured in points which are symmetri- 
cally located with respect to the base line in the photographs and to the line mt in the model. For 
the measurements of y-parallaxes in oriented models from approximately vertical photographs over 
rugged ground it is suitable to use some special arrangements in order to facilitate the location of 
the points. We assume the orientation performed so that by,=0by,. 
A mask can be placed upon one of the photographs (diapositives)!. For the measurements of y- 
parallaxes in the regularly located 15 points according to Fig. 3 there are five parallel slots in the 
mask about 5 mm wide, see Fig. 4. The 5'-coordinates of the photographs are defined by the center 
lines of the slots. The z'-coordinates are defined by the model points 15, 55 and 95. The detailed 
procedure for finding the correct points in the model is easy to realize. 
For the measurements of y-parallaxes in points on the fundamental circles for checking the radial 
distortion (see Fig. 3) two masks have to be used, one for each projector. The masks have to be 
constructed with respect to the requirement that the fundamental circles must be drawn around the 
principal points of the photographs respectively and that the points must be symmetrical around the 
/ 
(in the model). 
ND CO 
line x= 
L 
If the y-parallaxes are measured in the model (with by, or by,) it is most important that the flying 
altitude is determined for each point. 
1 See V. Gruber, O.: Kniffe und Pfiffe bei der Bildorientierung in Stereoauswertegeräten. Bildmessung und 
5 5 > 
Luft bildwesen 1938, 13, PP- 17— 26 and 13— te 
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