60 X 
  
  
  
  
  
  
Fig. 25 With 8094 forward overlap, the most favourable plotting models are chosen according to the terrain, thus 
permitting sufficient adaptability. 
The limiting scale of a map is decided either by the specified accuracy or by the smallest terrain de- 
tails - which must be clearly identifyable in the photographs - required to be shown on the map; on 
the other hand, the maximum flying height might be limited by the atmospheric conditions. The better 
the picture quality of the photographic camera, the smaller the minimum scale is for sure identifica- 
tion. In cases where the flying height is limited, e. g. due to cloud, haze or the aircraft's operation 
ceiling, the short focal length is an advantage since it is then possible to get closer to the required 
picture scale, and a larger area is covered per picture. 
Frequently, a favourable fitting to the map sheet is easier, which, with the given focal length, influences 
the picture scale and therefore the flying height as well. 
In using super wide angle photography, one should, however, also bear in mind the aspect of the ter- 
rain. In broken country, important details might be hidden because of the wide angular field. It is there- 
fore recommended that the overlaps be 80%, and that the models are chosen for plotting according to 
the nature of the terrain. Fig. 25 shows in the row (a), the overlaps flown at 80%. The aerial triangula- 
tion is carried out with the 60% overlapping series 1,3,5,7,... or 2,4,6,..., as seen in therow (b). Rows 
(c), (d) and (e) show how, according to the terrain, 80% overlapping models may be used for the plot- 
ting. Of course it is also possible to use the 60% overlapping pictures for mapping in the case of flat 
and open country. 
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