Commission I Presented paper 
Testing in Aerial Photography 
by F. L. CORTEN 
LT.C., Delft. 
Between the two world wars, photogrammetry developed in such a way that it became 
necessary to improve and check the air photo quality constantly, not only with respect to 
its geometrical and dimensional properties, but also with respect to its image quality. 
This need was satisfied in many countries with the aid of national institutes, such as the 
National Research Council in Canada, the Institut Géographique National in France, the 
toyal Aircraft Establishments in the U.K., the National Bureau of Standards in the 
U.S.A. ete. In addition, research laboratories of Kodak, Zeiss, Wild, ete., have been adding 
their knowledge and effort to promote aerial photography in various fields. The improve- 
ments in aerial survey are, to a large extent, due to the combined efforts of these 
institutes and they are also fully capable of carrying out any check or physical test 
required by the photogrammetrist. 
Still, there is a need for an international testing centre; not for reasons of impar- 
tiality but rather because certain gaps must be filled, particularly with respect to com- 
parison of products or methods from different countries and also because of the fact that, 
in many cases, the various measurements carried out by different institutes are often 
incomparable and cannot be interrelated with each other. This need also becomes apparent 
in various articles dealing with subjects of air photo quality [1], [2], [3]. 
In the future, tests carried out in this field by national or international institutes 
should preferably fulfil some special requirements in order to be wholly useful: The 
methods should cover the complete field of air photography in its various phases. Further- 
more, as it is virtually impossible for any single institute to cover the whole field, the 
test methods should be such that they can interrelate and amalgamate with results 
obtained elsewhere. Various testing criteria fulfilling these requirements are available. 
An obvious example in the field of quantity is the expression of deviations and errors as 
standard deviations or mean square errors; but also in the field of quality we can use 
generally accepted sensitometric methods and internationally standardized quality criteria; 
in addition, the contrast transmission function is now available as a correct physically 
descriptive and over-all evaluation of image formation quality [2]. Along these lines, it 
becomes possible to carry out individual tests which can be linked together in order to 
be representative for the complete performance of the air photographie procedure. 
Amongst many commercial and institutional research laboratories, there is a tendency 
to test according to criteria as indicated above. Also in this respect an international 
testing centre for air photographic matters can fulfil a task and at the same time it can 
stop such gaps not covered by the national institutes. One example is the need for 
comparison of film performance as indicated by J. A. Eden [1]. Another example is the 
evaluation of various positive copying and dodging printers. Such investigations are set 
up as comparative research but they may develop to consulting if the need arises. 
The I.T.C., Delft, — one of its tasks being to collect experience systematically, to 
study photogrammetric techniques and equipment and to compare their results — is 
prepared to act as such a testing centre. The need for this also fits into the scheme of the 
recently established I.T.C. Consulting Department about which some more detailed infor- 
mation will be published shortly. 
[1] Eden, J. A., The need for an international test house for air films. International 
Archives, Comm. I, London 1960.