The well-planned conference brought interesting aspects. A great number of technical papers were presented 
and later distributed as a composite volume. The paper by two of the authors above was dealing with the same 
subject. 
Many comprehensive viewpoints with a multitude of technical details concerning integrated planning of aerial 
surveys were discussed, but there were almost none on the economic aspects of such surveys, particularly cost 
calculations. 
In order to give a supplement in this respect, the authors aim at bringing the matter of survey cost to attention 
and to stimulate a discussion. As a base for their views, the authors use a simulated project, however, based 
on actual experiences. 
This project entails development of a complete ore deposit including mine area, ocean harbour and a 
connecting railroad and service roads as well. 
The photogrammetric activities have to be programmed from the very beginning to the completion of the 
project. This requires one or more aerial photographic survey with ensuing production of photographs and 
preparation of maps, etc. They have to be planned in relation to the map accuracy needed, step by step for each 
phase in the project. 
An important factor is that all costs in the photogrammetric context may be regarded along strict economic 
lines. 
4. Blansjaar, P.W.H. 
Eckhart, D. 
Geerders, P.J.F. 
van Kuilenburge, J. 
Seyhan, M.E. 
Netherlands 
A COMPUTER CONTROLLED PRECISION 
COMPARATOR-DENSITOMETER 
At the NIWARS information processing division a machine was developed and constructed which automati- 
cally measures densities of a photographic plate or film. The points of the plate to be measured are specified 
by a computer programme. It is possible from former measurements to compute the next (optimal) point to 
be measured. Separate density measurements are performed in 240 psec, the searching speed on the plates is 
limited by the allowed maximum speed of the comparator screws. The system is very flexible as the computer 
has a relatively large memory for this use (12 K words), and can be programmed in Algol-60. The basic 
components are a digital Philips-Electrologica computer, a modified David-Mann comparator and interfacing 
logic made by our group. 
The use of the machine envisaged is high precision measurements of plates and selective measurements of 
remote sensing images on film. Remote sensing processing tasks for which the instrument is particularly suited 
are compensation of large image distortions (e.g. in SLAR or IR pictures), on-line reduction of unwanted 
shadows (e.g. in false colour pictures), density-slicing (e.g. in correlation studies of ground truth and image 
contents) and all further applications where digital picture processing is of use. The beginning of test 
measurements was in the spring of 1972. 
5. Cazabat, C. 
France 
PROBABLE AVALANCHE LOCATION MAPS 
For the purpose of protecting towns and tourist and sporting facilities in high-mountain area, surveys of safety 
conditions and in particular of avalanche dangers are made in France. The mapping of probable avalanche 
concentration areas in the Alps and Pyrenees is being done by the Institut Géographique National. The basis 
for this mapping campaign is intensive geomorphological photointerpretation being done by a specialized staff 
and concentrating, in particular, on snow accumulation areas, reliefs favorable to the onset of avalanches, 
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