71 
We now generalize Bergenvik’s idea, by using more than four points, by using 
points not in the same plane, by using more than two pictures with different 
¿¿-values to define the interior orientation. 
8.5.1. Aerial Photography. 
A disadvantage of the method is that, in the case of aerial photography, 
oblique photography is not an operational condition, when we want to study 
vertical photography. An advantage is that atmospheric refraction is symmetri 
cal around the nadir point and the radial distortion is symmetrical around the 
principal point and as they do not coincide it should be possible to separate 
these regular errors under operational conditions. The same circumstances also 
cause unequal weights a priori for the image co-ordinates. If we disregard this 
and take two photos with ¿¿-values different by 100 g , if the geometric condi 
tions given in Fig. 23 apply, and if the interior orientation defined by principal 
point, principal distance and radial distortion is given by 
dr — a$r* + a 5 r 5 + a-j 7 
we then obtain the weight and correlation numbers for the interior orientation 
given in Table 15. 
This means for a standard error of unit weight j 0 = 6 //m that ¿.r () = s Uq = 5.3 
¡um and s c = 17.3 //m. As there are 25 points measured in the two pictures we 
Fig. 23. 
Two oblique pictures with 
the same orientation ele 
ments except for x, which 
differ 100® . Twentyfive 
points on a relatively flat 
ground then provide the 
weight and correlation 
numbers given in Table 15. 
have 2x2x 25 — 18 — 82 degrees of freedom.