GVII-8 
PHOTOGRAMMETRIC ENGINEERING 
Stereoscopic visual acuity of the human eye is perhaps the most critical 
human factor governing the detection of small objects from photographic 
images. The eye functions best for visual acuity when the diameter of the pupil 
is 4 mm. 
The power of mental acuity is associated with the training, experience, 
professional background of the photo interpreter, as well as with his powers 
of observation, powers of imagination and powers of judgment. 
All of these factors point to the need of carefully selecting photographic in 
terpreters, and to requiring rigorous eye examination prior to selection to such 
positions. 
One author, Moessner, states, that simple devices for testing stereo per 
ception has handicapped practicing foresters, geologists, engineers, and others 
who employ photo interpreters. Although many technical schools now include 
training in photogrammetry and photo interpretation, few have adequate 
classroom facilities for testing the stereo perception of their students. 
The floating-circles stereogram as described, is designed to be used with the 
inexpensive lens stereoscope, and furnishes a practical means for testing this 
rather elusive sense. It is an improvement over previously used stereograms 
since it provides a measure of the degree of stereo perception rather than merely 
giving a yes-or-no answer. 
The 171 tests which were made form the basis for a rating scale with a mean 
of 87.7 and a median of 92. Experience indicates that unless a student makes a 
grade of 80 or higher on the test, he will be seriously handicapped as a photo 
interpreter. 
Others point out that there is no single vision test that is completely ade 
quate, since the photo interpreter needs more than stereoscopic acuity. Among 
other requirements are: good distance vision, acceptable near vision, good re 
serves for accommodation and convergence, good extra-ocular muscle balance, 
and the visual capacity to maintain an exacting search for small details. A 
person having a very high rating in one of these vision tests, may prove on 
further testing to have the poorest over-all vision characteristics, from the PI 
standpoint. 
In the military field, selection of personnel for training in photographic 
interpretation is a long continuing problem. In many cases this selection has 
been arbitary with the result that those given training in photographic inter 
pretation often have neither the requisite qualifications nor the interest for 
the field. 
It has been suggested that the military would do well to draw their personnel 
for training from those who have had civilian education or experience in earth 
science or engineering. For example, in the U. S. Forces at the present time, it is 
estimated that there are about 1500 earth scientists in uniform, about half of 
whom appear to have assignments which do not utilize their technical back- 
grou nds. 
Since, in the civilian field, the demand for photographic interpreters exceeds 
the supply, civilian selection for photographic interpretation is generally done 
on the basis of the individual’s personal interest in pursuing the field. This 
method at least assures that the important factor of personal interest in the 
subject is present. 
TRAINING 
A professional field requires a professional man at the helm. Photo inter 
pretation is a professional field which may cross several professional fields and