16 
thing, confirm the very satisfactory results using only APR data. A second triangulation 
in a Stereoplanigraph C8 carried out by Fairey Air Surveys Ltd. of London gave similar 
results, proving that the input in this case is the limiting factor. 
4. Rhodesia Experiment (see [6]) 
ITC Research was interested in this triangulation, because it was its first application of 
the use of réseau camera. This was in this case of special interest because observations 
carried out before, proved the presence of considerable irregular film shrinkage. Its in 
fluence could be eliminated to a certain extent by the use of one réseau point next to each 
orientation or wing point. It was nevertheless not surprising that the residual parallax in 
all points had an average value of 12 microns, which was, however, only a fraction of what 
has been observed in several photographs as irregular shrinkage. The block adjustment has 
given remarkably good results, compared with the difficulties experienced in this aerial 
triangulation. The 13 planimetric ground control points were more of less along the edges. 
For height control five lines of control points, in total 92 points, plus heights of the 13 plani 
metric control points and 119 scattered water level points were used for block adjustment 
of height with the Jerie Analogue computer. The results are as follows. 
The absolute precision in height derived from the residual in the 224 height control points 
was given by a standard deviation of 3.3 m which is 0.27°/ 00 of the flying height. For the 
planimetric adjustment sections of 8 models were used with a result for the relative preci 
sion as follows: 
mu = 2.0 m = 0.17%o Z 
m x = 5.6 m = 65 ym 
m y = 4.7 m = 55 ym 
5. Sierra Leone 
This adjustment carried out as consultant for Philips Telecommunication made use of 
203 models, existing RC5 9x9 inch photography with principal distance 6 inch. The 
photographs were triangulated by KLM Aerocarto. Jerie height Block Adjustment was 
carried out by ITC. The survey consisted of 10 small blocks, the height control given by 
10 barometric points per block. The standard deviation of the residual errors in the control 
points was 1.5 m in height with a relative error of 1.0 m. Planimetric adjustment was 
carried out per strip on old slotted templet control, the height being in this case the only 
really important element. 
C. Aerial triangulation by the Photogrammetric Service of the Cadastre 
Although the Netherlands have a dense network of triangulation points from first to fourth 
order (7.7 per km 2 ), photogrammetric restitution still needs determination of minor 
control points with the proper location in each model. These points are at present deter 
mined by means of aerial triangulation. The total production can be derived from the 
following data. The total area increased in this period from 20,000 to 50,000 ha per year 
with scale of photography 1 : 2,500 tot 1 : 12,000 taken with RC7, RC5 or Zeiss convergent 
twin camera (see table 1). 
The triangulation is carried out in the Stereoplanigraph C8 with ecomat-coordinate 
registration of x and y, because the Netherlands Cadastral Service does not need to take 
into account the height of the almost flat terrain. 
The choice of the ground control points depends largely on the method of adjustment 
of the observations. Until recently only strip adjustment was used. Then in each strip six