studies the photographs thoroughly by means of a mirror stereoscope. The 
topographic interpretation of those photographs results in a drainage pattern 
on a special drainage sketch, which for a large area shows the relation between 
the various drainage details. During the triangulation in the A 6 various points 
of this drainage system are determined in altitude and may be used with good 
results as control data for the computation of the altitude. An article by 
B. Scherpbier entitled “The application of photogrammetry in Road Location 
in tropical areas", published in the Congress number of “Photogrammetria”. 
shows quite clearly that this method may be successfully used for the pro- 
duction of maps of tropical regions, to be used for road building and other 
engineering purpose. The comparison of the altitudes determined by ground 
survey and by the photogrammetric method described proves that the difrerence 
between the two results is of the same order as the local variety in the altitude 
of the trees, which determines the limit of precision of photogrammetric maps 
ot a jungle area. 
For theoretical studies in aerial triangulation see Report of Comm, III, 
pages 31, 40 and 52. The present reporter wishes to stress the importance of 
the publication by Prof. Roelofs at this Congress of material on the subject 
of the “Adjustment of aerial triangulation by the method of least squares’. 
On the basis of the technique introduced by Tienstra, Roelofs succeeded in 
deriving formulas for the correction of the machine co-ordinates x, y and z 
of nadir points and other points of a strip, based on 7 conditional equations; 
these may be divided into two different groups of 3 and 4. It seems that 
Roelofs has for the first time computed an adjustment system which is not 
only of theoretical, but also of practical use. 
CHAPTER IV — PHOTOGRAMMETRIC MAPPING. 
Instruments, Methods and Research. 
| The cameras used in this country during the last four years and by 
Netherlands agencies abroad have been indicated in Chapter I. The plotting 
instruments in use are as follows: 
Survey Department of the Ministry of Public Works: 
2 Zeiss Stereoplanigraphs 
1 Wild Autograph À 5 
1 De Koningh Rectifier 
3 Wild Stereoplotters À 6 
2 Radial triangulators De Koningh. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
   
  
  
   
  
  
  
  
  
    
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