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3. — GENERAL CONSIDERATIONS ON THE PROCEEDINGS OF AERIAL TRIANGULATION 
PER STRIPS WITH THE INSTRUMENTAL METHOD 
a) Anyone giving a glance at the tables, will get the immediate impression that 
the instrumental method per strips is the one most overspread; that is to say it is used 
by a very large group of photogrammetric Organizations. It is, however necessary to 
point out that triangulations per strips in comparison with triangulations per blocks, 
present a larger dispersion of operating proceedings, and a greater variety of purposes 
for which they are employed. Furthermore, in spite of its great variety, the proceeding 
per strips presents a definite shifting towards the application of medium and large 
scale cartographic problems. 
Very long strips occur very saldom: the tendency being towards short strips, or 
if long, cutting them up into short ones by a rather relevant series of ground point 
groups. 
In general, the length of the bridge span obtained by the bridging of photographs 
among the known ground point groups, does not exceed 10-15 photographs. 
Moreover, there exists, in practice, a general tendency to use aerial triangulation 
mainly with a view to supply a planimetric position of the points. 
Elevation-points are either obtained by adjustments based on a greater number 
of points, or even by levelling each model quite independently by means of a suffi- 
cient number of elevations points. 
The large variety of proceedings found in practice in this very sector to obtain 
a better altimetric precision, goes to show how much the precision demanded for ele- 
vation-points, is considerably more restricting than the one demanded for planimetric 
positions; and also how the precision demanded in elevation is by far superior to the 
one obtainable by scientifically experimented plans in photogrammetric research. 
As a new proof of the actual encreased difference between the demands and the 
precisions obtainable by aerial triangulation especially in elevation, there is the very 
large number of countries in which aerial triangulation is still under consideration. 
In those countries a search is still carried out to discover a method or proceeding 
consenting to reach a good enough precision to satisfy necessities. 
It is not our task here to find out whether demands are justified or not; as our 
right is only to point out a position of reality and facts causing a considerable delay 
in the application of aerial triangulation. 
b) We are now going to analyse separately the various phases of aerial triangu- 
lation proceedings by instrumental method. 
Flight. — In the field of flight there are no novelties or outstanding characteristies 
to be mentioned. 
The preponderance of wide angle cameras remains undisputed, however notable 
attempts of applying converging cameras have been started with fair results. 
About the tendency, already mentioned, of employing aerial triangulation per 
strips with the cartographie aim of medium and large scale detection, flights were 
made almost entirely within 1.000 and 6.000 metres of altitude. 
Higher altitude bridgings were executed with the sole purpose of studying and 
experimenting. 
The inner orientation determination, an element of essential importance in aerial 
triangulation, has not been taken care of in any special way. It 1s, however, worth 
mentioning the particular proceeding employed in several Northen Countries (Finland, 
15