36 
  
  
  
  
  
3 8 4 
A 1 x 17 2 
Td m bou 
d | ; 
I Fig. 2. Positions of 
i 5 9 6 Orientation points. 
  
From the basic formulae which express the analytical per- 
spective relationship of two planes, the following differential 
formulae, valid for vertical photography, can be derived: 
dx, = - Lada — zdx'j) 
1 ; 
dy = -.Ud, —dy'j) 
: ) 
dx, = ees —b)de, — £dx' y)] 
  
1 ; 
dy; = — (dern m7 
Into (1) have been introduced e; ze ce, xps, xXu-x—b 
and z; 2zj; —z. The origin of the coordinate system x, y, z is thus 
the left hand projection centre. 
If a reference plane, over which the flying height is z,, is 
introduced, then: 
z=29+Az (2) 
where Az is the variable height difference. 
A numerical relative orientation using 6 points, (Fig. 2), is 
assumed; for the points 3, 4, 5, and 6 
b | = (= constant) (3) 
is valid. 
Using the elements of camera IJ, the orientation formulae 
are: