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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.