1€ 
of 
je 
———— 
(477) 
experience with gyroscopes and we found that errors in the registration can 
have two sources. First, there are the vibrations of the plane that only can be 
eliminated by damping. The second group of errors consists of changes in the 
direction of flight. Even small variations have influence on the gyroscope. 
Only by flying-tests will it be possible to draw conclusions about the obtained 
precision. 
Mr. Nistri answers that his experiments will be carried on in the direction 
as indicated by Mr. Dubuisson. 
The president gives Prof. Zeler an opportunity to make some remarks 
referring to the question of triangulation. 
Prof. Zeller: 1 don't believe that the atmosphere is responsible for the great 
local-errors that are observed in the results of aerial triangulation. That would 
be the case if there occur turbulences very close to the lense, and this can be 
avoided. Besides these atmospherical irregularities would not only produce 
errors in single pictures but certainly very often in the strip. I rather believe, 
based on some years experience, that the source of these local errors is lying 
in the fact that a plate is not well supported by the frame of the camera. This 
may change the internal orientation considerably. (Small pieces of glass may 
get between plate and frame). It is also possible that the form of the terrain 
approximates a dangerous surface, which may prevent an accurate relative 
orientation. À second remark concerns the high precision restitution instru- 
ments. It seems to me that the introduction of a relatively small by or bz as 
well as a variation of bx of 10 or 20% should not sensibly change the systema- 
tical error of high precision instruments. This changement of systematical errors 
should anyhow not exceed the accidental observational errors. I refer to the 
strip of 100 km taken in Switzerland with the wide-angle Wild-camera con- 
taining 41 negatives with a flying height of 4600 m. After the compensation of 
the systematical errors the graph that may be seen at the exhibition shows an 
absolute accidental character of the residual errors in x, y and z. I therefore 
believe that the precision of an aerial triangulation and its economic output 
depend less on the used method but more and in the first place on the precision 
and the field of view of the camera and on the stability of the restitution 
Instruments. 
After a short summarizing of the discussions the president closes the meeting. 
FOURTH SESSION 
Friday September 12th 1952, 14.45—15.05 hr. 
Ihe president reads a preliminary draft of the resolutions and asks for 
remarks or comments from the floor. 
The resolutions were adopted with some small changes in the points B1 
and B2. 
General Hurault proposes to change the term *aerial triangulation" in 
“cheminement”. 
Ihe president is in favour of this proposal and asks for a translation in 
English. Perhaps the term *photographic traverse" could be used.