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We experienced in the Netherlands, as in some other countries that the great advantage 
of block adjustment, carried out by either method lies in the high relative precision which 
is obtained. Since this precision of short distances is in general in cartography more 
important than the precision of the absolute position of a point, it may be expected that 
this easy solution of the block adjustment will make aerial triangulation acceptable in 
many cases where at present only ground survey was used for the determination of control 
points in each pair. We think here in particular of large scale mapping for cadastral and 
similar purposes. 
In addition to the development of block adjustment we can mention this time in the 
Netherlands national report also important contributions in the improvement of the 
triangulation operation itself. 
The first regards analytical radial triangulation which has now been in regular use in 
the Netherlands for over 30 years with radial triangulators Zeiss and De Koningh. From 
the instrumental point of view we draw the attention to the new Wild radial triangulator 
after the design of Prof. R. Roelofs which found its definite from during the period, covered 
by this report. Without any doubt this instrument can be considered as an improvement 
compared with the older types, which after the second World War did not come back 
on the international market. 
The use of the method of analytical radial triangulation will be furthered also by a new 
method of computation developed in the I.T.C. by F. Ackermann and published in the 
first Congress number of Photogrammetria Volume XVI pages 81-90. The principle of 
the method is that he does not carry out an adjustment of the directions before computing 
coordinates but applies the least squares adjustment directly to the coordinates, with the 
possibility of introducing such simplifications as are in accordance with the required 
precision. 
D. Eckhart of I. T.C. has programmed this computation for the Stantec Zebra computer 
and for similar ponchtape machines. Roelofs will present a paper in Commission III 
informing the Congress about the results, obtained with the radial triangulation of a block 
to which were applied the Ackermann computation and the I.T.C. Jerie block adjustment. 
I consider both these refinements of the classical analytical radial triangulation to be 
very important since we can expect a more regular use of camera orientation equipment 
for the determination of the inclination of the optical axes. It will be possible to determine 
in the negatives the isocentre and the nadir point. This will enable us to reduce the con- 
stant errors in the directions to absolutely negligible amounts. This means that we can 
have the full benefit of the high precision of this method of measurement, comparable 
with that of the aerial triangulation in space. In all cases in which the photogrammetric 
map production needs only planimetric coordinates, the analytical radial triangulation 
with the modern means and block adjustment will become of the greatest importance. 
There are many such cases as for instance for cadastral maps and for all those projects, 
for which there is a discrepancy between the requirements of precision for planimetry and 
for heights to such an extent that the only economical solution is to determine the heights 
by normal ground survey. Irrigation and drainage projects are important examples of 
this situation. 
A further contribution to the development of aerial triangulation is given by Ir. C. M. A. 
v. d. Hout, Chief Photogrammetrist of the Survey Department of the Ministry of Transport 
and Waterstaat and part-time lecturer in analytical aerial triangulation at the I.T.C. 
Van den Hout developed a solution for the well-known problem which gives final results 
with a very small number of iterations, even in the case of mountainous terrain, combined 
with rather large inclinations of the optical axes. This method can be applied furthermore 
11