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CONVERGENT VERSUS VERTICAL PHOTOGRAPHY, DISCUSSION 123 
vertical cameras. Further, I have two slides here 
which can demonstrate the error-distribution in 
convergent models compared with vertical 
models; if there is time I can show these later on. 
Dr SCHERMERHORN: First we will give the 
floor to a few gentlemen who have asked for it. 
Mr A. L. Nowicki: My question to you is 
to ask permission to add something to Mr 
Thompson’s discussion on convergent photog- 
raphy. We have made some tests on 15 degree, 
20 degree and the Zeiss type of convergent 
photography. Our results, based on tests ranging 
in photography from 3,000 metres to 10,000 
metres and using many different first and second 
order instruments, have brought us to this 
general conclusion that at this time for a single 
model the convergent is perhaps 30 per cent 
more accurate than the corresponding vertical 
photography taken at the same altitude. How- 
ever, in the aerial triangulation phases of it there 
are quite a number of divergent values tested to 
date, and so far we have found that when the 
converging cameras themselves are not very 
accurately correlated as an entity in the plane, 
and with a very fine timing cycle of at least 
1/1000 second the aerial triangulation phases 
are inferior with convergent than they are to the 
vertical. 
However, some recent tests with a very 
accurate combined camera and a very accurate 
timing system have shown that the convergent 
aerial triangulation can be as well as perhaps 
50 per cent better than the vertical. However, 
the tests are so short and so few that we have 
not come to any general conclusion as yet, but a 
great deal more should be done on this matter. 
Herr Professor FINSTERWALDER: An meinem 
Institut ist eine Doktorarbeit gemacht worden 
von Herrn von Julsny, und zwar über eine 
Triangulation mit Vertikalaufnahmen und mit 
Konvergenzaufnahmen. Das Ergebnis war zu- 
nüchst das, dass die Konvergenzaufnahmen ein 
schlechteres Ergebnis hatten. Die Untersuchung 
ergab, dass die innere Orientierung nicht ge- 
nügend genau bestimmt war, und es ist festzu- 
stellen, dass bei Konvergenzaufnahmen der Ein- 
fluss von Orientierungsfehlern sehr viel unan- 
genehmer ist — es entstehen die Aufbiegungen 
und Fehler zweiten Grades — als bei Vertikal- 
aufnahmen. Nachdem diese Fehler festgestellt 
waren, wurde die innere Orientierung verbes- 
sert und dann war ungeführ dasselbe Ergebnis: 
es war ein Streifen mit zwanzig Aufnahmen und 
zwar aus der Flughóhe von 5000 m und die 
Normalaufnahmen hatten eine kleinere Brenn- 
weite als die Konvergenzaufnahmen. Es waren 
Konvergenzaufnahmen mit 30 Grad. 
Dr SCHERMERHORN: I have one other remark, 
which is this. We have at present many times the 
comparison of entirely different types of cam- 
eras. I mean, if you take the American Geolog- 
ical Survey, they are working with the wide 
angle and a very large angle of 30 or 40 degrees 
convergency. They compare vertical photog- 
raphy with the wide angle, but in Russia they 
are working with the super-wide angle and have 
been doing so for a long time. This changes the 
picture entirely in this problem of comparison 
because we must no longer compare wide angle 
photography with convergent, but in this case 
— and also Mr Thompson mentions this in his 
report and I put it in my publication — the tests 
with the super-wide angle are promising in this 
respect because there you have also a base/ 
height ratio of 1.0. Therefore that is another 
reason to say that we are at present not entirely 
sure and there remains the problem of the value 
of a type like the Zeiss Twin camera for large 
scale work. 
Mr M. PLOTNICK: Dr Schermerhorn said we 
ought to think a little about standing on our 
feet. So I would like to ask a naive question. It 
is in respect of the development of the super- 
wide angle, especially in aerial triangulation. 
What is the practical advantage of this method? 
I would join our American colleagues and would 
say that in big projects, not in single models, or 
operating single models and comparing them 
with the super-wide angle, but in a project which 
might have an accumulation of certain errors, 
minor and accidental and so on, we have to take 
all these into consideration and have a certain, 
I would say, commercial point of view, taking it 
more reasonably from the point of dealing with 
a great number of photographs and a great num- 
ber of models. I am sorry, I do not know this 
point so well. 
Mr N. Lzzr: I have only four things to say. 
Coming to the problems of the inaccuracies and 
instability of film material I would like to sug- 
gest that if research has been done, where is the 
point, where the film changes, while it takes in 
the air, in the processing or during drying or in 
other conditions. 
The second thing is, if the film is unreliable 
to such an extent, I think I foresee a change also 
in the building of cameras. Instead of using the 
glass plate as a reliable method, maybe the next