4 
projection plotters, I wish to illustrate here a special design of universal joint I have 
devised for the connection of the guide-rod to the photograph-holder and which. has been 
developed since some time. The joint is so designed that it is possible to introduce at will, 
and to the desired degree, an error of complanarity of the two axes in the cardan, so as 
to compensate for possible differences of film shrinkage in the longitudinal and the trans- 
versal directions. 
Advisability of applying such a joint to the Santoni's stereo-plotters, especially in 
connection with the development of aerial triangulation, shall be decided upon after 
experimental work in this field, presently being carried out under the auspices of the 
International OEEPE Organization, has been completed. 
Another device, still concerning the mechanical projection of the lines of sight, I 
gimbal system of antiflex-rod | | 
  
  
  
  
  
  
  
  
  
  
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Space-rod 
Fig.3 
designed and applied to the Stereocartographs Mods. III and IV, as well as to the Stereo- 
simplex Mod. III, is the balancing system of the guide-rods, I have named ''Antiflex". 
The principle of this device is shown in Fig. 3. Balancing is obtained by means of count- 
erweight P applied to auxiliary rod q supported by an individual gimbal and set parallel 
to the main guide-rod (either inside, or outside it). The auxiliary rod engages with the 
main guide-rod in » at an approximate distance I from the gimbal of the latter. It follows 
that bending which would appear in the main rod, consequent to its tilt from the vertical, 
is ineffective in section v in which it is geared to the balancing auxiliary rod. Deflection 
of the remaining rod sections is also negligible. 
On the other hand, the stress necessary on the joint coupling the rod to the Z-car- 
riage, to produce polar rotation of the former, is also minimized by a perfect balancing 
of the guide-rod. 
Insofar as rectilinear construction of the guide-rods is concerned, it can be said that 
within the limits of lengths in use at present, (600 to 750 mm), no appreciable sinusoidal 
bending has ever resulted. Only exceptionally, a general bending with a maximum of 2-3 
micron toward the center of the axis may occur, due to molecular setting, subsequent to 
the different thermic processes. Considering the widest changes in coupling joint position 
occurring for one stereogram, the effects of such bending, if any, are practically negligible. 
The efficiency of a mechanical projection plotter is easily established by the projection 
of two grid plates, using two spheric cams (for distortion-free lenses). After having 
'arried out the projection, separately for each camera, an appropriate base shall be ap- 
plied and the stereoscopic model prepared by the projection of the grids. 
The reading of d« dy dz deviations taken at the instrument scales, will show that in 
first-order instruments (such as for instance, the Stereocartograph Mod. IV and the 
Stereosimplex Mod. III) the lines of sight are reconstructed to the accuracy of about 
5 sec. 
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