8 
  
  
  
  
   
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    
the necessary projective operations must be executed in order to pass from the point 
considered to its homolog. 
We immediately declare that an analytical procedure could only be possible when the 
two conjugated image lines could be expressed with equations in photographic coordinates, 
which is obviously to be excluded in practice; therefore there only remains the analogical- 
  
  
S A + 
Fig.5. Genesis of nuclear fulera F, and F, upon the take dihedral. + + 
geometrical procedure that can in practice find two forms of expression: the graphic and 
the instrumental. 
It is necessary therefore to represent to ourselves, first of all, the take dihedrai 
developed in a plane (which will then be that of the drawing or that of the foundation of 
the instrument) with the frames of the two perspectives in exact reciprocal internal and 
external orientation, and the two nuclear points. The analogical realization of the cor- 
responding nuclear beams can be obtained, in the beforesaid representation, either by 
means of the tracing of lines or by means of orientable alidades that materialize them. 
However in practice a problem of scale arises. 
In fact, representing in a plane the photogrammetrical arrangement referred to the 
take dihedral, there will appear together, as has been seen, dimensions of a minor order 
(photographie) such as those of the frames and those of the coordinates of the nuclear 
points, and dimensions of greater order (topographic) such as those of the take components 
along the faces of the dihedral. 
To maintain the dimensions of minor order inside of photographic size, it is necessary 
to accept a limitation to the opening of the take dihedral and to the intrinsical asymmetry 
of the take, (as will be shown in Chapter II — d). Without this limitation the abscissae of 
the nuclear points (or one only), would be inclined to the infinite with the increase of the