GVII-16 
PHOTOGRAMMETRIC ENGINEERING 
Consistent with this definition, factors which are basic to photo interpreta 
tion are listed under two main classes suggested by Colwell. These are (1) 
factors governing the quality of the photo images and (2) factors governing the 
perception and interpretation of photo images. Under quality are characteris 
tics of color or tone, image sharpness, and stereoscopic parallax. Under percep 
tion and interpretation are characteristics of visual and mental acuity of the 
photo interpreter, his equipment and the techniques employed by him. Many 
of these factors have been or are being studied. 
Much work is going forward in the areas above listed; reference will be found 
in other sections of this report and in the reports of other commissions. 
One of the more interesting facets of photographic interpretation research is 
the recent emphasis on developing means for qualitative and quantitative 
evaluation of the results. The creation and application of such evaluation meth 
ods would go far toward making the practice of photographic interpretation a 
science rather than an art. 
PHOTOGRAPHIC INTERPRETATION KEYS 
Photographic interpretation in its various applications, is confronted with 
the task of producing information relative to many areas of human knowledge 
and endeavor. Therefore reference materials of a tremendously varied nature 
must be developed and made available in readily usable form. In the military 
services, where a single individual may be required to perform interpretation 
in many subjects, keys and other reference materials must be designed for use 
by all photographic interpreters, regardless of the educational or specialized 
background of the individual. 
In the civilian field, the field of reference is not normally so broad for any 
particular individual. However photographic interpretation keys, carefully 
prepared and properly used, are found to be of use in many programs. A point 
to be kept in mind is that keys are not a cure-all for all photographic interpreta 
tion problems, nor are they a substitute for professional training and experience. 
The development of keys has been proceeding at a steady rate during the 
reporting period. Of interest has been the continued development in the United 
States of “mechanical” type (punch-card) keys for identification of man-made 
objects. 
Very little objective testing of the effectiveness of keys has been performed 
to date. This should receive high priority in the future. 
RESEARCH PROJECTS ARE ON THE MOVE IN AGRICULTURE AND FORESTRY 
In forestry, new techniques are being investigated. Photo volume tables are 
being constructed. The use of larger scales is being explored, as well as several 
combinations of film and filters. Effects of season of year are being studied for 
the purpose of increasing the efficiency of the U. S. Forest Survey. Studies are 
also considered or under way to examine accuracy of stand height measurements 
in the Rocky Mountains. Studies of dot sampling bias on contact photos in 
mountain regions are under consideration. Aerial photo stand volume tables 
are being constructed; these will greatly aid photo interpreters in forestry. 
Research in forest insect surveys is undertaken by the U. S. Forest Service 
to develop methods for conducting such surveys from the air. Both visual and 
photo methods are investigated for detecting and appraising forest insect 
damage. Studies are conducted on sample strips of Ektachrome or Anscochrome 
film. The instruments used are the Ryker or Old Delft mirror stereoscopes. In 
formation studies involves area of insect damaged timber, number of trees