Norway, Sweden) of verifying in flights the inner orientation of photogrammetric 
cameras (distorsion, above all) by photographs, taken at different altitudes on ice-co- 
vered lake at the time when the ice is melting. 
In this way, from the altimetric deformations of the model that should be per- 
fectly plain, one can reach back to the distorsion anomalies of the objective lens when 
shooting. 
Concerning auxiliary instruments, namely those instruments permitting to bring 
about some data related to camera orientation at the moment of shooting, we have 
to point out as follows: 
a) Their use is very seldom occuring and this, only in the case of exceptionally 
longer strips than normal 
b) the instruments preferred are those permitting to give a positional element, 
instead of an angular one. The most used ones are: the statoscope; the altimetric radar 
or A.P.R.; the Shoran and Hiran methods (these latter in America above all). The 
other auxiliary instruments, including the solar periscope, are mostly used during a 
scientific research phase. 
c) an auxiliary instrument datum is often used only as an extra check of flight. 
Ground points. — Something has already been said about this subject in the general 
premisses of the present paragraph. Giving now more details, it is necessary to mention 
the fact that no cantilever strips have been carried out. Also cases of strips having 
points only in the extreme models, namely without ground points on intermediary 
ones are very rare, whilst in general there is at least one point, or a group of points 
in the strip centre. 
Altitude points are generally much more numerous than planimetric ones. 
Bridging operations. — Instruments. — Practically all instruments are em ployed 
to carry out aerial triangulation — The so-called first-class instruments (provided with 
a base-bridge) are generally ased to carry out the bridging of the photographs. 
Instruments of a minor order and deprived of a base-bridge are used for carrying 
out aerial triangulations, but following special proceedings, such as the one of indepen- 
dent models method. Multiples are also used for small-scale cartography. 
Information gathered state that the instruments go through some very careful 
examinations and adjustments, before being employed for aerial triangulation; yet 
only rarely this accurate setting of the instrument reaches the point of the altimetric 
projection control execution; often limiting itself to the determination of instrumental 
zeros and the planimetrie errors through an independent grid projection. 
The proceedings of work followed by the different Organizations, also vary. 
Many instruments can be worked with one operator only, while others instead 
require many operators in a sequence of 2 or 3 shifts. It is quite impossible to find 
statistical correlations with the different working criterions employed and the results 
achieved. 
Scarcely relevant are the news about the bridging proceedings and orientation- 
method concerning models. On the whole, rapporteurs have ignored this topic. 
Data collected allow us to state only that in the scale of bridging proceedings, the 
largest use is represented by the free bridging; conditioned bridgings employing stato- 
scope data (aerial levelling) or the A.P.R. system are following. 
The application of the bz constant method is very limited, whilst numerous 
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