U.S.A.-4 PHOTOGRAMMETRIC ENGINEERING 
grids indicate possibilites of accuracies at least two to three times as great as 
those obtained in our tests with aerial photography. Therefore, at present the 
studies are being concentrated upon possible sources of error in convergent pho- 
tography and upon means for eliminating or nullifying such errors, In connec- 
tion with these studies we have been most fortunate to have had the aid ol 
such eminent and internationally known photogrammetrists as Professor Hal. 
lert, Professor Roelofs and Dr. Brandenberger. Through the contracts with The 
Ohio State University Mapping and Charting Research Laboratory the assist. 
ance of these talented scientists has been made available to Fort Belvoir and 
has been of great value. 
Much work remains to be done on the development and evaluation of wide. 
angle convergent photography. In addition to the work with Kelsh Plotters and 
Multiplex, we are investigating the use of C-8 and the A-7 for aero-triangulation; 
the results are quite promising. Work remains to be accomplished on simplifica- 
tion of procedures and techniques of triangulation. The methods used at present 
admittedly require a high degree of skill. Investigations are now being made of 
the advantages to be gained from block adjustment of the convergent tri- 
angulation strips and optimum ground control distribution patterns. A very 
interesting test along these lines is planned. In the Southwestern part of the 
United States there is a test area consisting of a square—thirty miles long 
and thirty miles wide. At approximately every mile, in the manner of a reseau, 
there is a well defined control point the coordinates of which are known. This 
area is being photographed simultaneously with a vertical and convergent 
installation; it is hoped with this photography to complete a thorough and 
impartial investigation of the differences to be expected with vertical and con- 
vergent compilation and aero-triangulation. 
Before bringing this paper to a close, perhaps it would be appropriate to 
make a few observations on the general subject of the use of convergent photog- 
raphy in mapping. Some thoughtful criticisms of this method of aerial photog- 
raphy have been made. It has been pointed out that low altitude photography, 
particularly for cadastral work, over urban areas, would produce blind spots, 
areas of no stereo-coverage, if taken with wide-angle convergent photographs 
with a base to height ratio of approximately 1.2. In the Corps of Engineers, 
U. S. Army, there is no argument with this point. Using convergent photog- 
raphy for low altitude mapping, cadastral or otherwise, is not planned. Con- 
vergent photography is being studied at Fort Belvoir as a high altitude mapping 
procedure. It is believed that no one system of mapping can answer universal 
requirements. One might almost try to design a single method of transportation 
that would meet all requirements. The photogrammetrist or photogrammetric 
engineer earns his professional status by virtue of his ability to determine the 
best method, when presented with given conditions. A common criticism of 
convergent photography is the inconvenience of using contact photographs 
prepared from the aerial negatives. This could be a serious inconvenience; how- 
ever, it is relatively simple matter to design a transforming printer which will 
produce nominally rectified prints almost as quickly, if not just as quickly, as 
contact prints. À more interesting and recent comment is that the introduction 
of a super wide-angle lens will make wide-angle convergent photography rela- 
tively obsolete—just as the wide-angle lens terminated interest in the conver 
gent-narrow-angle photography. The idea of an acceptable super wide-angle 
mapping lens is very interesting. Our position on this question may almost be 
considered an enviable one. We represent no commercial organization, nor do 
we profit in any manner if one system should prove to be better than another, 
  
   
  
   
  
   
   
   
   
  
  
   
   
  
   
  
   
  
  
   
   
  
   
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    
except th. 
tion for 0 
opinion pi 
tial as a « 
with othe 
need. The 
angle lens 
photograf 
To sur 
but comn 
map large 
a high de 
To solve s 
flying and 
indicate t 
if converg 
the conve 
aero-trian. 
can say tl 
raphy wit 
accuracy. 
our findin: 
by our scie 
of not mal