70 PROBLEME DES BAUINGENIEURS, DISCUSSION 
Discussion 
Mr B. HALLERT: First I want to mention 
in a few words that this summer Professor 
Borchers from Ohio State University, USA has 
been travelling Europe for stereoscopic photog- 
raphy of architecture, in particular baroque 
architecture but also a great number of fea- 
tures of cultural and historical interest. Un- 
fortunately, he could not come here to tell us 
something about his experiences, but he has 
given a paper to the Congress which I think is 
of great interest. This application of photogram- 
metry to the cultural and historical problems is 
most important and should be taken up in many 
places. 
I would also like to mention that we have 
been performing a series of special investigations 
of different types of cameras and instruments for 
the creation of central projections in general. We 
have used what we call the grid method, which 
means that the instrument or the camera is used 
for photography of regular grids which are 
determined with high accuracy. This method has 
been used for aerial cameras as well as for 
microscopes, X-ray instruments, television 
images, etc. I have here a number of copies of a 
preliminary publication of these results and 
these can be taken from the table below. 
It seems very important that we concentrate 
upon the determination of the standard error of 
unit weight of image co-ordinates in different 
cases, in addition to the determination of sys- 
tematic errors, for instance, radial distortion. 
Dr Schmid's paper was certainly very interest- 
ing and illustrates one of the applications of this 
technique, in this case to cameras more or less 
for astronomical purposes. Further, there is a 
paper entitled “Results of Practical Investiga- 
tions into the Accuracy of Aerial and Terres- 
trial Photographs", (presented to Commission I) 
which may be of interest for the determination 
of the weight distribution within single photo- 
graphic images. We found there from aerial 
cameras and other cameras that there is a con- 
siderable difference in the weight of the image 
co-ordinates from the centre of the plate and to 
the edges, which is quite natural because we 
have the individual interpolations of the plate 
itself. 
Finally, I want to say a few words about a 
paper which Mr Helming is presenting to you in 
a few minutes. This is a typical example of one 
of our first duties when we are going ahead with 
photogrammetric measurements of any kind. 
We have to concentrate upon the quality of the 
actual instrument and the photographs taken 
with that instrument; that is very important. 
Herr Prof BURKHARDT: Ich danke Herrn 
Kollegen Hallert und ich glaube, wir dürfen 
jetzt zunüchst einmal von Herrn Helming hóren 
interessante Untersuchungen über die Bestim- 
mung der inneren Genauigkeit einer Messkam- 
mer. Ich glaube, dass besonders die Ausfüh- 
rungen von Herrn Helming für uns alle sehr 
interessant sind. Meistens haben wir ja unsere 
Kammern vorher gründlich untersucht, bevor 
wir anfangen zu messen. Aber es zeigt sich, dass 
das fast in allen Fállen unbedingt notwendig ist, 
Ich darf Herrn Helming bitten, mit seinen Aus- 
führungen zu beginnen. 
Mr R. HELMING: At the Division of Photo- 
grammetry, Royal Institute of Technology, 
Stockholm, distortion for terrestrial cameras are 
determined from photographs of a test field. The 
test field consists of symmetrically located and 
accurately determined. points on a wall. The 
distribution of the points is principally the same 
as in Grimeton ( Fig 2a in Prof Hallert's paper 
to this Congress: Results of Practical Investiga- 
tions into the Accuracy of Aerial and Terrestrial 
Photogrammetry). By this method all influences 
of the camera on the reproduction of the bundles 
of rays are taken into account. 
A test of a phototheodolite, f — 152 mm, 
this summer resulted in a distortion curve which 
did not at all correspond to that quoted by the 
manufacturer. The combination camera body — 
glass plate — plate holder was scrutinized as 
indicated in my paper: Control of and Improve- 
ment on a Phototheodolite, f — 152 mm. 
Thereby the reason for the deviations men- 
tioned was found. 
From what I have later on seen at the tech- 
nical exhibitions of this congress, the manufac- 
turers customarily does not seem to consider 
that nonsatisfactory construction of the plate 
holders may ruin the performance of the best 
lens. 
Herr Prof BURKHARDT: Ich danke Herrn 
Helming für seine ausserordentlich nützlichen 
Ausführungen. Meistens stehen wir ja, wie ich 
schon angedeutet habe, in der Konkurrenz mit 
anderen Messverfahren, und wir können un- 
sern Kollegen meistens nur helfen, indem wir die 
äusserste Genauigkeit in unseren Messungen 
walten lassen, und ich glaube, es wird sich sogar 
empfehlen, eine entsprechende Resolution hier 
noch vorzubereiten, dass bei diesen Arbeiten 
  
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