The knowledge of the »osition of NY Dey ec ye center of the photo 
gram is obtained when the parameters X^ /, Y\ /, 2\ /, &, S ,&, are known, 
We shall now examine the angular parameters. o 
We shall call à , sy qi,» the angular parameters which define the po 
sition of the internal syStem in the point O. We shall indicate with 9 , 
y Wy the angular parameters which define the internal system in any" 
point P with respect to the internal system in the point O. We shall define 
the following three parameters; 
da 
These three parameters being defined, we shall be able to deduot the 
position of the internal system in any point P, based upon the position of 
the internal system in O with the 
Et Pa TR) Pad 
The computation of the space reseotion should therefore furnish the 
12 parameters; 
o o o 
x 2, y! } 7 M c, S ,9, J, Po’ a” A, B, C, 
3,3 - EQUATIONS OF EXTERNAL ORIENTATION OF A PHOTOGRAM. 
We are now able to find the relations which connect the 12 desoribed 
orientation parameters to the quantities measured indirectly on the photo 
grams, or else to the internal direction tangents t , t or t, t. 
The orientation equations will express the fact that the infernal 
tangents of direction, transformed into the ground points system by means 
of the orientation parameters should be equal to the direction tangents 
computed by means of the ground points coordinates and of the perspective 
centers of the photogram. As a reference system for the equations we shall 
take the already defined rectangular system XYZ, which has the plane XZ pa 
rallel to the vertical plane containing the vector S. The coordinates of 
the ground points are given in the system XpYpZp. In such a system the per 
ss Te Qo Uer poor pates of the photogram corresponding to ( ) 0 m) 
Xn , Yn ; Zip . Those of any perspective center Xo P , Ys P ’ Am P , 
Y 
and those of any point of the ground X Z 
TU Tuo. 
We have 
xq P) = xj) +X SXp 
  
X125, 
and 
wher 
tive 
angu 
d