Incidentally, the January, 1964 issue of Photogramme trie 
Engineering includes two articles particularly pertinent to 
this discussion. One by Mr. F. J. Doyle [4] is a history of 
the development of analytic aerotriangulation including a 
splendid set of references. The other by Professor Gracie [ J] 
is an exhaustive bibliography of articles in English on the 
subject. 
Acceptance of Analytic Aerotriangulation 
As recently as four years ago only a handful of photogram- 
metrists were confident that analytic aerotriangulation was 
feasible, it is now generally accepted as a useful tool. 
Although some still do not fully accept the improved accuracy 
as an established fact, the proponents point out that accuracy 
is no longer limited by the unavoidable mechanical restrictions 
inherent in conventional stereotriangulation instruments. 
It seems correct to state that virtually no purchase of a 
conventional first-order instrument is now made in U.S.A. 
without carefully considering the possible application of 
analytic systems. 
One must recognize that the speed of analytic aerotriangula 
tion is usually inferior to that of the plotting instrument. 
At present, one trades speed for accuracy. However, speed 
may not actually be a factor in the future. First, as I just 
mentioned, accuracy can be exploited in order to use a greater 
flight altitude which, in reducing the number of photographs, 
may effectively make the speed entirely comparable. Secondly, 
speed will surely improve as more experience is gained and 
as improvements are made in the measuring equipment inasmuch 
as the practice is still in its Infancy. 
The Monocomparator 
It seems now to have been firmly established that accurate 
aerotriangulation can be performed through the use of a 
monocomparator and that a stereocomparator is not an absolute 
necessity. One must hasten to add, however, that the work 
can be done somewhat more accurately and more efficiently 
with the stereocomparator. My colleague, Mr. Charles Theurer, 
has developed this discussion further in another paper else 
where at this Congress. 
The application of the monocomparator has aided in a 
practical way in the establishment, development and popularity 
of analytic aerotriangulation because of the economic problems 
associated with the relatively high initial cost of the stereo 
instrument. The future may well change this economic advantage 
of the monocomparator: the advantage may only be temporarily 
associated with the immediate transitional problems relating 
to the establishment and development of the new system. It 
may well become evident that over a period of more than three 
years the stereocomparator is actually less costly in view