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The method of execution of the large-scale aerial triangulations which the Com- 
mission has decided to adopt, is the so-called free method, but based on the nume- 
rical perfection of the relative orientation. 
The tests do not only allow the determination of the precision obtained by this 
method, but also the drawing of conclusions as regards the increase in precision 
of the method, resulting for instance from an improvement of the relative orien- 
tation, the correction of deformations of the model when joining the couples, the 
influence of the density and the distribution of control points in the models, the 
use of the lateral points, the use of auxiliary instruments, etc. 
The use of auxiliary instruments (statoscope, solar periscope, etc.) when taking 
the photographs has been judged to be very interesting. Provisions have been 
made to use them during the flights as extensively as possible. 
The experimental polygons. 
Austria, Switzerland, Italy and Germany have offered their collaboration for the 
realization of experimental polygons for the work of Comm. B. It was thought 
advisable that the first efforts of the Commission should begin with the exploi- 
tation of the Vorarlberg-polygon, already prepared by Austria. Owing to its 
position this terrain lent itself well for an extension of the flights which had to 
be organized by the Swiss Group. 
Below please find more detailed information on: 
The Austrian Polygon. 
It is situated in the zone of Alstatten (Switzerland) — Hohenems (Austria), the 
most western part of Vorarlberg, on both sides of the Rhine valley which forms 
the frontier between the two countries. 
The terrain to be photographed spreads, without important unevenness, in its 
north-western part and partly on hills in the south-east; the absolute altitudes 
vary from 450-500 to 650-750 m. 
The first photographic coverage carried out by Austria has seven parallel strips, 
orientated south-west/north-east, of a variable length, viz: 
4.7 km for strip 1 
15 , >, Etrips 2 and 4 
16 ” ” ” 3 
S39 5 » » 5, 6;and 7. 
The average distance between the axes of the strips is abt. 1250 m. This is suf- 
ficient to ensure satisfactory lateral overlaps. 
The signalized area is about 5500 ha and there are about 600 control points. 
The preparation of the terrestrial points has been carried out by using the 
Austrian basic triangulation as a base for the determination of many triangulated 
points of a lower order, and by precision levelling on the chosen polygon. 
The signalization of the points was well done and the centering of the signs was 
executed with an average precision better than 2 cm. 
The engagements accepted by the Centres with regard to work for the different 
Commissions have induced the Commission not to stimulate the formation of new 
polygons intended for large-scale triangulation tests. 
However, the Commission and the Comité Directeur have agreed to take up again 
in the course of 1956 the investigation of the offers of new polygons to be carried 
out by Germany and Italy. 
This decision, taken after consultation with all those Centres engaged in the 
work of Commission B, can easily be explained when taking into account that the