14 
  
   
  
   
   
   
   
  
  
  
  
  
  
  
  
  
   
   
calculation on formulae that would risk to become quite complex and above all non- 
universal. 
The consideration of the take dihedral instead permits it to reach a set of formulae 
in a system of intrinsical reference, that prescinds namely, from the absolute orientation 
of the model to plot and is good for whatever take arrangement characterized by con- 
vergency of the take axis in the limits of use of the homolog-comparator. 
  
  
  
  
  
a * * — 
T 
* 
> 
< 
"8 
9 
S + - 
a 
* > 
+ m 
  
Fig.8. Intrinsic axis system of the take dihedral. 
The object to be plotted is referred, that is to say, to the carthesian trine having 
the origin in the intersection of the three planes (Fig. 8): 
— the nuclear flight plane, namely, that YZ nuclear plane parallel to the edge of the 
take dihedral; 
— the plane of the normal section, namely, that XY plane normal to the edge of the take 
dihedral that contains, at least, one of the take centers: for example the left one for the 
person looking at the object to be surveyed; 
— the profile plane, namely, that XZ plane normal to the flight plane which includes 
the edge of the take dihedral. 
Obviously such a reference system goes to automatically identifiy itself with the tra- 
ditional symmetrical one, when the base and the take axis are horizontal. When the base 
is horizontal and the take axes are equally elevated (e, — ¢,) the horizontalization of the 
plotted model is obtained by means of a simple rotation about the nuclear axis. 
Generally the horizontalization will be made by rotating the reference system (as shall 
be indicated in the subsequent lecture) by two rotations one around the Z axis in order