3 
analyzed in terms of its individual operations to an extent 
required to satisfy the scrutiny of even the most skeptical 
critic. Such investigations show that, theoretically, the 
method of aerial triangulation should provide accuracies 
which satisfy at least lower-order geodetic control require 
ments and indicate, among other results, that, in principle, 
photogrammetric triangulation is superior to classic geodetic 
triangulation concepts, due to the fact that with the latter 
the observed quantities cannot be related directly and 
rigorously to the geometrical model to be determined. 
From the standpoint of the data reduction process there 
are no serious deficiencies in the comparators used to 
measure the image coordinates. A variety of instruments 
with adequate internal precision and accuracy are available. 
One may as well be satisfied with the economy of the measur 
ing process, although there is room for improvements which 
could directly influence the overall economy of the method. 
From the foregoing remarks, one may conclude that neither 
basic geometric principles nor the evaluation equipment-- 
including the computational means provided by electronic 
computers--impede the photogrammetric method in the attempt 
to establish geodetic control. By virtue of elimination it 
is, then, obvious that the process of taking the individual 
photographs must be the critical operation. However, reso 
lution characteristics of today's high-performance lenses, 
in combination with optimized emulsions, are not to be blamed. 
The overall metric quality of these lenses--that is to say, 
their adherence in terms of projective qualities to mathe 
matical models for the simulation of specific photogrammetric 
bundles--is, as we shall see, quite adequate. In addition to 
more conventional approaches, a novel and attractive solution 
to the problem of determining systematic film distortions is 
now available. This provides a cluster of fiducial marks 
covering the whole area of the photographic record by pro 
jecting reference marks which are an integral part of the 
lens system. For strictly geodetic control determination, 
one may, however, prefer to circumvent this problem by using 
sufficiently thick glass plates, an operational procedure 
made feasible by the size (roominess) and performance charac 
teristics of modern airplanes. 
When talking about establishing geodetic control points, 
at least two reasons exist for signalizing all such points 
with high-contrast targets. Such a procedure apnears unavoid 
able in order to assist in the identification problem. Equally 
important, only high-contrast targets will produce hard 
imagery which, not unlike star point images, show energy dis 
tributions closely resembling square wave patterns.