TT Er TITRA 
CHET 
  
  
   
88 REPORT OF COMMISSION VII 
etc. Strongly exaggerated reliefs are disturbing in the mountains, unnatural, im- 
possible and absolutely wrong forms result therefrom. 
3) Time of Taking the Photographs: For the interpretation of the cover of 
the ground a high solstitial point is generally desired, as it presents the least risk 
of veiling caused by cast shadows. The relief of the ground is, however, plasti- 
cally pronounced, in medium latitudes, only in air photographs taken in the 
fore- or late afternoon. Here also early or late exposures lead to too great veil- 
ings caused by shadows. The most suitable time of the day depends on the forms 
of the relief as well as on the season or latitude. 
4) The Season for taking Air Photographs: Exposures in winter with the 
ground being covered with snow show the relief forms, the structure of rocks 
etc. generally more distinctly than exposures in summer, but they do not allow 
of clearly recognizing the coloring of the ground or the vegetation. Therefore 
air photographs taken in different seasons are desirable for a good many pur- 
poses of interpretation. The choice of the time for taking air photographs of 
any area should be the result of careful examination both of the ground and of 
the specific purposes of the interpretation. For Switzerland a combination of 
winter's end (February/March) and late summer (August/September) generally 
appears to be the most favorable time. 
5) Supplementary Oblique Photographs. For purposes of interpretation 
the vertical photographs should, if ever possible, be supplemented by a series 
of oblique photographs. Such a combination would render very good services 
in the exploration of the surface of the earth. 
6) Quality and Enlargement of Photographs: Highest sharpness of the 
picture is desirable also for purposes of interpretation, for air photographs are 
often observed with the help of magnifying glasses or used after strong photo- 
graphic enlargement. Enlargements of photographs greatly facilitate the inter- 
pretation. Sharp photographs are, moreover, much more economic than blurred 
ones, for they allow — with the same final effect — of relatively greater flight 
altitudes and, consequently, of covering a larger area with a smaller number 
of photographs. In this connection we may be permitted to point out the 
prominent optical qualities and the hitherto unequalled resolving power of the 
new objective “Aviotar” of the fully automatic plate camera Wild RC 7 (Heer- 
brugg, Switzerland). 
7) Coloured Photographs: For purposes of interpretation the coloured 
photograph (same definition of the picture presupposed) has proved superior to 
the non-coloured photograph. Coloured photographs show the structure of 
woods and fields, the colourtone of the ground, kinds of settlements, age etc. 
much more clearly than monochrome pictures. 
Of all kinds of pictures the coloured stereophotograph is the nearest 
approach to nature. In Switzerland the coloured photograph has not been 
sufficiently tested up to now. 
8) The Interpretation of Air Photographs and the Reconnoitring of the 
ground: Only he who examines the local conditions on the ground itself can 
obtain a maximum profit from the interpretation of the air photographs. The 
air photograph, and in the first place the air stereophotograph, however, permits 
of restricting the reconnoitring of the ground very strongly, approximately to 
less than 5%: A provisional preceding interpretation of the air photograph 
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
   
  
  
  
  
  
  
  
  
  
   
  
    
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