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below have very much influenced the practice of photogrammetry and their importance 
will not be restricted to the Netherlands. 
We will deal in this chapter with the following subjects: 
111.2. Development of operational techniques. 
111.3. New developments in the theory of aerial triangulation and its adjustment. 
111.4. Aerial triangulations carried out by Netherlands organisations. 
III. 2. Development of operational techniques for radial and aerial triangulations 
1. Radial triangulation. 
The weak point in radial triangulation was so far the lack of a registration of the observa 
tions. Through cooperation between Prof. Roelofs and KLM Aerocarto a method has been 
developed to overcome this difficulty. Starting with registration on a tape recorder, this 
method was improved by registration of the observations on mark-sensing cards which are 
directly transferred on punch tapes. The tape recorder is still used, but only to register 
additional information and for a further check on the main system. This method works 
quite satisfactorily with KLM Aerocarto. 
2. Aerial triangulation with the use of analogue machines 
In principle the operational methods are still the same. Although the modern block adjust 
ment does not require triangulation in strips for planimetry, in all cases in which height 
adjustment is also required, the normal operation in strips is still necessary. In those cases 
in which only planimetric coordinates are required as for instance for high precision 
cadastral aerial triangulation, independent models are used which are as such the basic 
elements for the block adjustment without the necessity to combine them first into strips. 
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3. Analytical aerial triangulation 
In the ITC which is the only organisation in the Netherlands which can carry out analytical 
triangulations, there is very little change in the operational technique on the Wild Stereo 
comparator which, so far, had borne the main burden in the application of this method. 
The only change in this respect was the introduction of a floating mark with a diametre 
of 60 microns, with the aim to have such small differences in size between the floating 
mark and the pricked hole, that stereoscopic fusion of a pair with only such a hole in one 
diapositive, would not be influenced unfavourably by too strong light around the floating 
mark. Although furthermore entirely independent movements of the left and right hand 
plate holders are easier, we found that an experienced operator gets used to the in series 
iterative setting which must be necessary if the pricked hole is in the right hand plate 
holder. The stability of this stereocomparator proved to be excellent during the past years 
of its continuous intensive use. 
111.3. New developments in the theory of aerial triangulation and its adjustment 
The following outlay of the various theoretical activities will be subdivided into: theoretical 
development of methods and theoretical and experimental investigations of precision of 
aerial triangulation and adjustment methods.