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GEOMETRISCHE EIGENSCHAFTEN DES BILDES, DISCUSSION 57 
is not intended to restrict improvements or ne- 
cessarily changes in calibration techniques. It is 
always important that, with a standard, it 
should not hinder progress. However, I would 
not like this to be used as an excuse to depart 
from the specification where it was not really 
necessary, and I think it is most important that 
we should make use of this recommendation as 
widely as possible in order that different labo- 
ratories will agree with one another. 
Also in the preamble, a paragraph has been 
added to point out the importance of providing 
complete identification data for cameras. We 
have emphasised the desirability of making 
resolution tests with the same sensitive materials 
as have been used in actual practice, and a sta- 
tement of the maximum resolving power of the 
photographic material has been required. Some 
references are given to methods of obtaining 
such data, we have reduced the significance at- 
tached to average resolving power and empha- 
sised the need for complete resolution data over 
the field. 
A note has been added on the differences 
which occured between laboratory calibration 
and the service use of a camera. We have defined 
average radio-measured distortion as a step to- 
wards defining a principal point of best sym- 
metry. Although the principal point of best 
symmetry is now defined in the recommenda- 
tion as a new term, it should be understood that 
the principal point of autocollimation and the 
distortion relevant to it remain the basic items 
which must be reported. Additional data is op- 
tional. 
It is now required quite definitely that the 
filter which is normally used on a camera 
should be in place during calibration. A state- 
ment of radial distortion along each diagonal 
is now required as well as the average of these. 
A completely new section, Part 5, on devia- 
tion of filters and camera port glasses has been 
added. This, I am afraid, is largely a Canadian 
development, but we have found tests of this 
sort very useful and I think it may be helpful if 
other people avoid the mistakes we made when 
starting such tests, 
Those are all of the important revisions. The 
reporters know that there was a vote taken on 
whether we should include the word ‘principal’ 
in the principal point of autocollimation and 
principal point of symmetry. The vote was 
slightly in favour of retaining the word ‘prin- 
cipal', and the present revision is written that 
way. 
In conclusion, I would like formally to re- 
commend that the draft revision dated 26th 
August, 1960, be adopted by Commission I and 
submitted, I believe, in the form of a resolution 
at the Plenary Session of the Congress. 
Mr J. A. EDEN: I have two short comments 
on two brief papers, the first on calibration cer- 
tificates. I contend that statements of distortion 
and principal distance which are all one normal- 
ly finds on a calibration certificate are not fun- 
damental measures at all, and are obtained only 
after various processes of distribution, interpo- 
lation and waiting. These tend to hide the ac- 
curacy of the measurements from which they 
are derived, and I put in a plea that the cali- 
bration certificate should list the basic meas- 
urements of x and 8, or whatever they may be, 
the angles of change of the lens and the meas- 
urements on the plate to which they correspond. 
There are, of course, no objections to the certi- 
ficate also listing various distortions and prin- 
cipal distance if the photogrammetrist is pre- 
pared to pay the calibrating authority for this 
work that I think he should be able to perform 
himself. But it is only by knowing the actual 
measures of x and 0 and the location of the 
points that were measured that the photogram- 
metrist can form an opinion of the adequacy 
of the calibration measure and how far he can 
apply these to the work he has in mind without 
unacceptable interpolations. 
The other comment I have on my second 
paper is that I have treated on the subject of 
air films. I feel that with air films there is a 
tendency for people to be very conservative and 
to stick to the brands and types that they are 
used to without inquiring whether or not there is 
available a more suitable brand or type for their 
purposes. This, I think, is rather to be deplored. 
It is not, for example, the case with cameras. 
Here people go for the best cameras; in conse- 
quence of this a great many cameras in use 
today tend to come from one or two firms. The 
other firms are thus continually striving to im- 
prove the quality of their cameras; this is a very 
healthy state of affairs of particular benefit to 
the photogrammetrist. To obtain the same state 
of affairs with films we need to be able to assess 
the comparative performance of all the different 
manufacturers’ products and brands, of which 
there are legion, and so compare the perfor- 
mances in speed, contrast, resolution, keeping 
qualities, consistency of patches, anti-static pro- 
perties, maintenance stability etcetera. I would 
like to suggest that the Congress should recom- 
mend the need for some international test on 
how to do this work and how to publish its re- 
sults for the benefit of all the users of the films