-J 
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al 
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vy 
nd 
ae 
et 
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Z 
Fig. 4. Usual arrangement of coordinate systems and rotations in terrestrial photo- 
grammetry. 
Such differential formulae must be developed around the actual 
values of the elements of the internal and external orientation. For 
approximately vertical photographs we can put 50 =x=0. Under 
these circumstances we find from the formulae (8) and (9), for instance, 
h hx' x 27 xy hy’ 
dx de’ — —de+—dh +1 + M y — — hdo + — dx 
C e C e c C 
(18) 
h hay y xy y"? ha' 
dy dy’ —de4+—dh+—Me— {1+ — hd e — —- dx 
c e C e 2 C 
(19) 
These differential formulae are of fundamental importance for the 
theory of errors of aerial photogrammetry with approximately vertical 
photographs.