Figure 1. 
A difference in lens height (dz) ac- 
cording to the figure gives too low 
values for measurements at the left 
side of the model and too high va- 
lues for measurements at the 
  
  
  
  
  
Figure 2. 
A difference in nadir point level ac- 
cording to the figure gives too low 
values for measurements at the left 
side of the model and too high va- 
lues for measurements at the 
right side. right side. 
Table 3 
/ 
Errors in 25 of h caused by differences in lens height or nadir 
h, d- h, 
as 
bi, + bY, 
h 
point level, p! calculated 
) 
  
  
Differences in lens Flying altitude 
height or nadir 
point level 2 500 4 000 5 000 
25 1-54 0.0, d 05 % 
50 o" 1.95 9; 10% 
100 4% 20 97 2 % 
200 8 9; 5 97 4° % 
In the actual test fields there are no great differences in 
elevation. The Östad field is the most hilly of the fields and the 
terrain is roughly divided into two levels, the difference between 
which is 50—60 metres. It has not been judged possible to take 
this fact into consideration. The errors in the results due to this 
fact are most marked for the flying height of 2500 m and as- 
suming that the calculated flying height is referred to an aver- 
8