(206) 
togrammetric definitions, preferably multi-language, could not be achieved 
within the time available. This should be part of our programme for the 
coming period. 
With sections 3 and 4, dealing with the measurement of the illumination 
of the focal plane and with veiling glare, I can agree completely. 
Reviewing the specifications as a whole, we can say that our work is not 
yet finished, because for really comparable data we need an internationally 
standardized single procedure. The work could not have been finished, because 
for attaining this we still need much more basic knowledge about what happens 
exactly in the formation of the photographic image, and we need more exper 
ience of how the proposed methods will compare and how they will work out 
in practice. Only after we have more fundamental knowledge and more ex 
perience will we reach our ultimate goal. The great merit of this specification 
is that it enables us to obtain this experience. Therefore, I may readily advo 
cate the adoption of the underlying proposal. 
Mr. J. E. Odle, England: 
A manufacturer’s approach to instruments for air survey is governed by 
practical considerations. Proposals to adopt International standards are there 
fore welcome and even if it is not possible at this meeting to arrive at conclu 
sions which will satisfy everyone, the discussion should clear misconceptions 
and ensure standardization of meaning, if not practice. 
Our Photogrammetric Laboratory undertakes the following optical work 
and while not strictly relevant to camera calibration some thought should be 
given to the problems cited since they may negate the constructors’ efforts. 
(a) Testing aircraft camera windows for homogeneity 
(b) Testing filters for: 
(1) transmission 
(2) homogeneity and parallelism 
(3) scale accuracy of correction wedges. 
We have issued standardized camera calibration certificates for the last 
seven years. 
Commenting on the draft proposals in detail: 
1.3.4. Cobb: We use two bright lines on a dark background. 
2. Calibration: We agree that the photographic method of calibration is the 
most desirable because of its approximation to the real conditions of use. On 
the other hand, providing precise techniques are used, we have found no 
significant difference in the results of photographic and visual calibration, and 
in fact we now use both techniques. On a production line basis there appears 
to be a definite time advantage in visual calibration, and in contradistinction 
to our thoughts on the subject a year or so ago, we are now tending towards 
visual calibration. Our confidence in the interchangeability of both methods is 
based upon detailed comparative testing carried out on three wide angle 
cameras in collaboration with a different laboratory, and independent obser 
vers. The differences revealed were of the order of microns. Under this section 
I would also comment that many of our users return their cameras for calibra 
tion each season. Consequently we have confidence in the repeatability of our 
results, and the ability of the air survey camera to maintain constants.