and 8.6 ¡um. Using Bartlett’s test we test the hypothesis that they are equal. The 
test gives an almost significant difference among them. A difference can be 
explained in the following way. The standard error of unit weight includes the 
errors of the co-ordinates of the test object. This test object is not the same for 
the three pairs, as the grid has been in three positions in every exposure. The 
positions are determined by the glass scale of the A6 and the setting may have a 
standard deviation of some hundredths of a millimeter. The movement may not 
be straight and this introduces errors in the co-ordinates. If the movement is not 
perpendicular to the glass plate this is compensated for by the parameters (prin 
cipal point and nadir point) in the adjustment. Such lack of perpendicularity 
will result in systematic errors in the parameters. This problem has been treated 
in [30]. 
8.2.6. Exterior Orientation 
The elements of exterior orientation are given in the co-ordinate system of 
the test object although this is not of particular interest. But the relative orien 
tation of the cameras and the base (see below) for every pair of pictures can be 
computed from the exterior orientation. This will be discussed a little. 
Testing the variation of orientation elements, it must be remembered that 
they are correlated. This correlation is sometimes very strong e. g., between 
principal point and rotations, between camera constant and distance of photo 
graphy. This holds for vertical photography and examples are given in Tables 
1—3. For oblique photography, which is the case here, the relations are diffe 
rent. In Table 8 a correlation coefficient matrix of the parameters is shown 
as an example. In this case we want to test the constanc of the interior and re 
lative orientation and the base. As the elements are correlated in all combina 
tions there is no simple test available to study the variation between pictures, 
and at the same time take account of the algebraic correlation. Therefore, 
each orientation element is studied separately, i. e. we use the corresponding 
marginal distributions for the tests. The variance between the pictures is deter 
mined from observations that are independent of each other. The variance wit 
hin pictures is determined from the separate standard errors of the correspon 
ding element. The values of the elements, their standard errors and the analyses 
of variance are shown in Tables 11 and 12. The test between picture pairs 1 and 
2 is introduced as the same aperature, f:45, was used. 
8.2.7. Interior Orientation 
In this case the interior orientation has been defined by five elements, x 0 Jo 
c as «5. Radial distortion and camera constant are inseparably related to each 
other, because a small change in the camera constant can be converted to a 
radial displacement. This is evident from the relation