ly clear (in some cases clouds and cloud shadows are accepted up to 5 per 
cent of the image surface) or entirely cloudy (high and thin clouds). The 
latter case is acceptable for aerial photography from low altitude, 
3.1 How are the geometric qualities of the photographs (the negatives, 
contact prints and diapositives) tested and demonstrated according to 
for instance points 3.11 - 3. 15 below ? 
3.11 The principal distance (camera constant or calibrated focal 
length) and the position of the principal point. Which tolerances 
are required at the determination of these data ? | 
5.12 Other systematic disturbances of the perspectives (radial and 
tangential distortion, affinity, asymmetry). 
Which tolerances are required at the determination of these 
systematic disturbances ? 
Are the effects of the earth^s curvature and of the atmospheric | 
  
refraction included in the radial distortion? 
3.13 Is the effect of the aging of the photographs upon the systematic 
disturbances tested? 
3.14 What is done in order to reduce or compensate the systematic 
disturbances of the photographs ? 
3.15 If compensating plates or similar devices are used at the printing | 
| 
or plotting of the photographs, how is the effect tested? Which 
are the tolerances for such devices ? 
27 answers. 
Camera constant (calibrated focal length): In 9 organizations corrections 
are regularly applied with respect to the shrinkage of the film. Tolerances 
are of the order of magnitude 0.01 - 0.02 mm for vertical photographs. In 
one organization the accuracy (tolerance ?) 0.005 mm is used for convergent 
photographs and for vertical photographs which are to be measured in a 
stereocomparator. 
Principal point: In all organizations the principal point of the photographs is 
determined from the fiducial marks or from marks in the focal plane glass 
plate according to the camera calibration. Tolerances between 0.01 and 0.05 
mm for the position of the principal point are mentioned. 
Other systematic disturbances of the perspectives (radial and tangential 
distortion, affinity, asymmetry) are mainly determined from laboratory 
tests of the cameras. Affine shrinkage of the photographs is usually deter- 
mined from measurements of the distances between fiducial marks (reseau). 
As tolerances for the determination of such systematic disturbances 0.01 to 
0.03 mm are mentioned. In 4 organizations the influence of the atmospheric 
refraction and earth^/s curvature are included in the radial distortion. In 
one organization the influence of the curvature, only, is included.