38 
is not yet possible to draw up a plan of utilization of the strips thus obtained. 
However, the German group of the OEEPE intends to utilize shortly the flights 
executed with the Zeiss RMK 21/18 camera, at present being thoroughly exami- 
ned with a view to making copies from it, necessary for the tests. 
Topographic determination of the control points. 
The systematic study of deformations which occur during the formation of a 
chain of models in the different restitution instruments requires that there are 
available a large number of well-identified points on the plates and in the terrain 
of which the coordinates in space have been determined beforehand. 
With a view to an efficient organization of work a great number of points of the 
Austrian polygon have been signalized, while making quite sure of the position 
and the centering of the signs. 
The location of the signalized points has been chosen in such a way as to have 
at one's disposal for each strip, at least one point with a known position near the 
nadir of each photograph and two lateral points, these being placed on the line 
which passes through the nadir and which is perpendicular to the axis of the 
strip. 
The other known points allow the verification of the joining of the models, either 
in the longitudinal direction of the strip or laterally, between opposite models 
of different strips. 
At the start of each triangulation there is available at least one special test pair 
(couple témoin) in which the number of signalized points to be observed is rather 
large. 
According to the instructions given, this couple must be entirely restituted during 
the tests. The differences between the coordinates determined on the ground and 
those observed by the instrument, will permit a study of the deformations of the 
first model and their influence on the development of the triangulations executed. 
Naturally, elements for the start of the triangulation which are given to the 
Centres before the commencement of the triangulations, are very limited, the 
imposed working conditions are given in detail in paragraph 8. 
The choice of the signalized and of the natural points to be observed during the 
restitution, was a task which had first been entrusted to the President of the 
Commission. 
In order to speed up the work it was executed on the Austrian polygon by Direc- 
tor Prof. K. Neumaier, because he had locally at his disposal all data relating 
to the signalization, to the topographic survey and also the photographic prints 
relative to the flights executed either by Switzerland or by Austria. 
The chosen points were indicated on a general index map. These have been sent 
as copies to all Centres engaged in restitutions. 
The numerical data relative to the topographic determination of the control 
points are indicated on lists which are kept by Prof. Neumaier and the Comité 
Directeur. 
Even the President of the Commission himself has no access to these lists: this 
measure of the Comité Directeur guarantees the seriousness with which the work 
is executed. 
The trigonometric determination of the coordinates of the ground points surveyed 
by methods already mentioned, has been executed under conditions which ensure 
a high average precision. Prof. Neumaier has indicated that the precision obtained 
on the Vorarlberg polygon was about 2 to 3 em in planimetry and altimetry for 
all surveyed points.