COMMISSION HP F1 | 
INT. ARCHIVES OF 
/, Vol. Xil:4 1956 
  
  
Appe ndix to the 
PHOTOGRAMMETR 
  
Communication to 
VIII International Congress for Photogrammetry 
Reprint from 
Svensk Lantmateritidskrift 
Commission 11 
ABOUT MECHANICAL RADIAL TRIANGULATION 
by P. O. Fagerholm, Sweden 
Some general conceptions 
The densening of a sparse geodetic network of control points in order 
to get sufficient number of passpoints in each photograph or each ste- 
reomodel is one of the main problems in modern photogrammetry. This 
point densening can be a question of horizontal and vertical passpoint- 
determination or only of horizontal. For the first purpose only instru- 
mental stereophotogrammetric bridging or related numerical methods 
can be used; for the second purpose also the different methods of radial 
triangulation can offer good solutions. The limitation for the radial 
methods — that they can only give horizontal positions of pass-points 
— seems, at the first glance, to exclude them in many cases, but other 
factors, advantages and disadvantages for both groups of methods must 
also be taken into consideration. 
Topographic maps (e. g. in scales 1:50 000—1:4 000), which shall be 
used for planning purposes, must have a rather good height-accuracy, 
especially in flat, slightly broken or rolling terrain where drainage, 
road-building and many other factors are very dependent on the relative 
and absolute elevation. If bridging is used for z-point-densening a cer- 
tain and rather big part of the permitted z-error of the final map must 
be reserved, not for the mean square error but for nearly the maximum 
error of the bridging. The reason is that the maximum z-errors are very 
likely to be found somewhere in the middle of a strip resulting in a 
plotting-model beeing lifted up or lowered down with nearly the amount 
of that errors. This reduces the margin for the z-error of each plotting 
model which decreases the permitted photography altitude. A lower pho- 
tography altitude calls for more strips and a greater number of triangu- 
lation models between the geodetic points. As the triangulation strip de- 
formation increases more than proportionally to the number of models 
between geodetic controls, the photography altitude must be still more 
decreased. If the elevation accuracy specifications for the final map are 
  
  
  
  
  
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