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As regards the vertical control it was found that a lack of sufficient ground control is 
one of the main problems in the plotting of contour maps in tropical areas. The data 
were derived from various sources, such as existing maps and reports and also from the 
levels of the sea, rivers and lakes. 
In some cases radar altimeter diagrams gave rather good results when controlling each 
strip. 
Secondary control for plotting was obtained by aerial triangulation, slotted templet 
triangulation and by a combination of stereotemplets with A 6 triangulation. 
The vertical control was also derived from aerial triangulation and in many cases 
checked by the drainage pattern, as mentioned in previous national reports. 
Regarding the general trend of development it is stated that the electronical methods 
for the determination of adequate ground control are regarded as highly promising. As 
to the plotting techniques these services believe that the use of scribing at the plotting 
table appears to be the most efficient. 
Further research should be carried out in particular on the application of the various 
types of camera orientation instruments and equipment for camera stabilization. 
Furthermore it should be considered to be of the utmost importance to carry out research 
work on the use of photograph scales between 1 : 70.000 and 1 : 125.000, obtained with 
the super wide angle camera in combination with camera orientation equipment, for the 
production of small scale topographic maps. 
I might add to this that this research project should also be extended to digital aerial 
triangulation on this very small scale photography for the determination of secondary 
control points, necessary for the production of topographic maps in scales 1 : 50.000 and 
even 1 : 25.000. 
These organizations are not in a position to provide us with a reliable estimation of 
time and cost data. A rough estimation of the percentage distribution of some elements 
of the officework is as follows: 
Preparatory work including aerial triangulation 409%, 
Plotting of details 43% 
Neat drawing or scribing 17% 
The preparatory work also includes the flight planning, the preparation of the photo- 
graphy for the aerial triangulation and plotting, and the triangulation itself. 
Subcommission IV.4. Fundamental problems 
The reporter for Commission IV.4 has answered a great many questions put forward 
in the questionnaire, which, however, have in many cases also been included in the reports 
of the previous Commissions. Consequently this sub-section of cHAPTER IV will not be 
complete and deals only with a number of special remarks. 
Regarding cameras it is considered desirable to have tolerances for the flatness of the 
focal plane frame as well as for the pressure plate in film cameras. I might add to this, 
that it is not sufficient to represent the perspective qualities of the lens and camera body 
by one distortion curve, obtained as the average of the distortion over different diameters. 
Viewing the high precision of stereocomparators and the application of digital photo- 
grammetry it is necessary to know the irregularities in these distortion curves, in order to 
obtain an impression about the residual errors which occur after introducing an average 
distortion curve in the digital system. 
The effect of compensating plates and similar devices is being tested by measurements 
in the model with redundant control for the absolute orientation by measuring accurate 
29