11 
The programme, which internally got the name “Anblock” achieves the block adjust 
ment simultaneously. It operates on the direct solution principle. This programme works 
very efficiently and successfully, a considerable number of blocks having been computed 
already. The use of the Anblock programme is at present somewhat restricted due to the 
small storage capacity of the Zebra computer. However, blocks consisting of several hun 
dred models can be handled directly, the actual number of models depending somewhat 
on the shape of the block and the number of points involved. Thus, at present the method 
meets all Dutch needs and, besides at Rijkswaterstaat and ITC, is also being used at the 
Cadastral Service and Topographic Service (see III.4). Following his search for systems 
of linear relations Van den Hout succeeded also in setting up a directly solvable system 
for blocks of radial triangulation [41]. 
Independently of this approach the mathematical department of the ITC has developed 
a programme for planimetric blocks, the units of which come partly from precision plotters 
(models) and partly from radial triangulation measurements. Using the latter data only, 
the method gives a block adjustment procedure for radial triangulation. This programme 
(“Ranblock”) is at present in operation for the Topographic Service (see III.4.E). 
At present some other investigations are being pursued concerning the analytical block 
adjustment of heights. It is too early, however, to report about results. 
In this connection a theoretical study of Ackermann may be mentioned who compared 
several approaches to block adjustment. He has shown that various approaches to block 
adjustment lead essentially to the same type of computational problem, the coefficient 
matrices of the equations to be solved being of similar structure [7]. 
C. Precision of strip and block procedures 
During the period 1960-1964 a number of studies have been carried out concerning the 
theoretical precision of strip and block adjustment depending on the triangulation proce 
dures applied and the control information used. 
Williams (Thesis ITC) has compared the theoretical accuracy of several methods of 
strip formation. H. G. Jerie has studied the accuracy of strip triangulation with the use of 
auxiliary data considering several types of auxiliary data and various weight ratios [45]. 
F. Ackermann has studied similarly the accuracy of the ordinary aeropolygon-strip-trian- 
gulation in combination with least squares strip adjustment and strip adjustment with 
interpolation methods of the polynomial type. In both cases various distributions of control 
points have been considered. In this context the polynomials of higher degree have been 
shown to be unsuited for strip adjustment, see [2], [3]. The investigation of G. Belling 
(Thesis ITC) was concerned with the use of composed polynomials of 2nd degree for strip 
and block adjustment and a comparison with the block adjustment method of G. H. Schut. 
With the help of the ITC-Jerie Analogue computer for heights, using its property to yield 
weight coefficients, H. G. Jerie has shown the theoretical precision of block adjustment for 
heights, for various control configuration [46]. He also has theoretically studied the effect 
of using composed sections in the planimetric block adjustment [43]. A study into the 
accuracy of graphical smoothing procedures for the adj ustment of auxiliary data is on its way. 
Besides these purely theoretical investigations some experimental investigations have 
been carried out into the accuracy of strip and block adjustment procedures. Back in 1960 
M. Spitzer tested a controled block (from Australia) with the ITC Jerie Analogue Com 
puter for heights in various control distributions [112]. 
Recently extensive statistical investigations into the precision of strip adjustment (F. 
Ackermann) and block adjustment (D. Eckhardt) have been carried out, the results of