gained already before the war and on studies about the propagation of random errors. 
We came to the conclusion that there was only one possibility to improve the precision of 
the results of aerial triangulation and to limit the necessary number of ground control 
points, namely to apply some method of block adjustment. Already before the War the 
author applied, through systematic lateral comparison of the adjacent strips, a kind of 
primitive block adjustment, which was published in 1940. In addition to this, Zeller has 
introduced a method of block adjustment by computing cross strips and applying a method 
of correction which, like the Zarzycki method, was a consequent application of the principle 
of interpolation. 
A more consequent method would be to introduce the condition of equal coordinates in 
each point of the total block of models, in common to two or four surrounding models. 
The introduction of all these condition equations could strengthen the whole field of 
models in a considerable way and replace a great percentage of the usual ground control 
points. It is well-known that the solution of this problem leads to a great number of 
normal equations, which is, even with high speed computors, a considerable amount of 
work and rather costly for a large block. Nevertheless convinced of the great advantage 
of block adjustment, attempts are being made in several places to find an acceptable 
solution along these lines; the I. T.C. is also trying to contribute to this approach. F. Acker- 
mann is preparing a thesis in which he presents a solution. 
The other and so far very successful method was developed in the [.'T.C. in the previous 
three years by Dr. H. G. Jerie, who designed two analogue computers; one for the adjust- 
ment of planimetric coordinates and the other for height. The theory of applied mechanics 
gave him the basic principles for his computer. Since it has been described in full and 
several publications have informed the photogrammetrists about its possible performance, 
it is not necessary to go into details in this report. The equipment has been patented by 
the I. T.C. and Dr. Jerie in several countries. It is produced by the I.T.C. workshops and 
has so far been delivered to about 20 services and scientific institutes. The advantage is 
not only that it gives the same precision as that which can be obtained with the purely 
analytical solution, but in particular that no further special means are necessary and that 
the execution of this adjustment does not require very high skill of the operator. It is 
obvious, however, that the quality of the observed coordinates determines the limit of the 
precision which can be obtained with the adjustment. It also holds that with this equip- 
ment no adjustment ever can compensate for bad observations. One of the great advan- 
tages, however, regarding the quality of the observations is, that for the adjustment of 
planimetry the famous discussion about systematic, accidental and pseudo-accidental or 
pseudo-systematic errors can be forgotten. The influence of each of these errors in the 
units, which are subject to adjustment in the block adjustment, are so small, that they in 
general disappear against the normal observational errors. Only in the adjustment of 
heights the strip functions as such. Therefore in that case it remains necessary, to give a 
correction for systematic errors to the observed values of height before starting the adjust- 
ment of the random errors through the whole block. For this correction a regular second 
order curve will do. 
It is very likely that in the near future we will see side by side the use of this analogue 
computer for block adjustment and the full analytical solution with the use of high speed 
computers. The latter method will be possible in a few of the big services, provided with 
this kind of machine, and the analogue computer will be very useful for the smaller 
services and institutes which have so far only a limited experience with aerial triangula- 
tion, having the benefit of the simplicity of the use of this equipment and of the easy check 
of all irregularities and gross errors in the observed coordinates. 
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