emen t LA 
  
  
  
  
In the applications of photogrammetry with which we deal here, the scale of the 
photographs is often determined by the possibilities of interpretation and will therefore 
be rather large (e.g. 1 : 30.000 or 1 : 40.000) with respect to the map-scale (e.g. 1 : 100.000 
or 1 : 200.000). If the map accuracy should be 0,1 mm the corresponding errors at photoscale 
are 0,5 mm, whereas the triangulation may give a relative precision of 0,02 mm on photo- 
scale. Therefore it has sense to look for a method which makes use of this excess of 
precision, without being too elaborate and maintaining a reasonable absolute accuracy. 
The purpose of this article is to suggest a method for a rational adjustment procedure 
that has the above property. 
It is based on the assumption that the high relative accuracy per model allows the 
connection of a number of short parts of different strips into one coordinate system, using 
simple linear transformations, without the accumulated errors surpassing the tolerances for 
the map. 
The blocks so-formed will always have a limited dimension and may contain for instance 
20 or 30 models. The exact number of models in each block will of course depend on the 
  
— 
zT 
Block boundaries 
  
Strip number 
Fig. 1. 
accuracy per model and on the map-scale. For a special case an experimental triangulation 
to determine the best size of the blocks will perhaps be recommendable. The connection 
of the blocks to one coordinate-system is the next part of the problem. This can be solved 
by using slotted templets. The slotted-templet method is indeed the only one which takes 
into account — be it mechanically — all conditions that have to be imposed for a 
theoretically correct planimetric adjustment. These conditions can be described generally 
as: After the adjustment, common points between blocks should have only one set of coordi- 
nates; terrestrial points should have the given positions. 
In normal radial triangulation the accuracy is limited by tilt of the camera-axes or by 
elevation differences in the terrain. In our case however, these sources of errors are elimina- 
ted automatically during the spatial triangulation. New errors are introduced when we use 
linear transformation formulas for the formation of the blocks but the number of models 
per block should be chosen in such a way that these errors can be neglected. 
The discrepancies that can be expected during the lay-out are therefore small so that 
deformations of the templets will be smaller than normally obtained and consequently the 
relative position of the points in one block will be better. 
To increase the resulting accuracy, it is recommended to devote the utmost care to 
every step of the method e.g. to use excellent material for the templets, etc. In this way the 
  
    
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