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