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(182) 
in flight. Consequently, all our photogrammetric equipment and procedures 
are based upon making the best out of photography which is blessed with all 
kinds of a’s, ¡3’s, y’s, (p’s, co’s, and other gratuities of doubtful quality. They 
distort the beautifully simple diagram of a true vertical central perspective as 
it is shown within the first three pages of almost any textbook on photogram- 
metry. Did you ever think of what would happen to the following 200 or 2000 
pages of our photogrammetric textbooks if we could limit our geometrical 
considerations to such a fundamental diagram, or, if we could base all our 
instruments and procedures upon such a simple relationship, forgetting about 
those distorting Greek letters? — An unrealistic thought at the present time, 
but still very inspiring, and possibly not so unrealistic if you are willing to go 
along with me on a second thought and possibly add some of your own. 
Strong efforts have been made in the past by several groups of photo- 
grammetrists to obtain information on the spatial position of the optical axis 
of aerial photographs by recording data during flight. Without trying to be 
complete, I may mention the two best known to me: Nenonen’s attempt to 
combine synchronous horizon photographs with aerial photography and 
Santoni’s efforts to record solar positions as a means of determining the in 
stantaneous angular position of the optical axis. Although locally successful, 
neither one of the methods has been generally accepted as a solution to the 
vertical problem. The question arises, why is that so? 
It certainly is not possible to answer this question within the very short 
period of time which is available here and the answer anyway should be dif 
ferent depending on whether the commercial or the military viewpoint dom 
inates the consideration. Approximately twelve years ago the United States 
Air Force accepted the trimetrogon system as the standard system for military 
charting. Although two cameras amply cover the wide angle desirable for 
military charting, the triple system was adopted because it included the horizon 
on opposite sides transverse to the line of flight. At that time, it was hoped 
that horizon photography would considerably simplify the compiling proced 
ures for military charts. No doubt, there have been occasions where the 
horizons could be used advantageously but the general hopes put upon the 
system were disappointing. It turned out that, under conditions of military 
operation, the information supplied by the horizon photography was not 
reliable enough to base a compilation system upon it. The trimetrogon compi 
lation system, therefore, does not deviate considerably from normal, but 
generally uses the photographed horizons, if available, to improve conditions 
of conventional radial triangulation. 
The Santoni system, in its present form, imposes a strong restriction upon 
the direction of flight lines. This is the main reason why it is not acceptable 
for military aerial photography. Commercially, this system may be satisfactory 
in areas where the restriction on the flight conditions can be accepted in 
addition to those restrictions provided by Mother Nature in forms of non 
photographic weather. 
The development of equipment which permits reliable tracking of celestial 
bodies other than the sun in bright daylight may open new angles for develop 
ment along the line of the Santoni system. It is questionable, however, whether 
such systems, though theoretically possible, will find wide commercial applica 
tion. The intricate electronics involved preclude economic considerations at