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PHOTO INTERPRETATION PICTURE, COLWELL 109 
  
Fig. 15. Two photographs of a three-dimensional model on which timber 
stands similar to those in Fig. 14 have been simulated, as described in the 
text. Note that on the left photo stand B appear to have much larger trees 
and a much greater volume than stand A, because B is nearer the camera. 
Actually, as shown on the right photo (taken after both stands had been 
placed the same distance from the camera lens) the two stands have identical 
sizes, densities and volumes and occupy identical areas. (Compare with 
Fig. 14.) 
5. Photo interpreters should learn to use to maximum advantage the pertinent informa- 
tion available to them from other fields of study. 
As the photo interpreter encounters new problems he should ask himself, “Is this a 
problem entirely peculiar to the field of photo interpretation or is it simply a new mani- 
festation of a problem which has been previously dealt with in related sciences?” With 
surprising frequency he will find the latter to be the case, and can profit accordingly. 
Thus, by borrowing from the centuries-old experience of plant and animal taxonomists, 
he may avoid many pitfalls in the construction of photo interpretation keys; by borrow- 
ing the precise terminology of the mathematician or engineer, he may avoid the con- 
fusion which would result by introduction of his own jargon for describing shapes, pat- 
terns, and other characteristics of photograph images; by borrowing measurement tech- 
niques from the photogrammetrist he may better be able to identify objects; by borrow- 
ing the search techniques, used by microscopists when they are studying slide specimens, 
he may learn improved methods for the systematic search of a photograph; and by 
borrowing from the experience of oculists, doctors of medicine, and psychologists, he may 
gain for the first time an accurate insight into the physical and mental characteristics 
which are so critical in making a good photo interpreter. Such mass-borrowing of infor- 
mation is not a shameful practice, but an intelligent one. Furthermore, the photo inter- 
preter can find consolation in the fact that for each bit of information he borrows, he 
offers repayment a hundred fold to those many fieds which are finding photo interpre- 
tation to be the most reliable and economical source of much of the information which 
they so vitally need. 
Conclusion. 
In concluding this paper, just a in beginning it, I have found it interesting, and I 
hope helpful, to extract information from the Commission VII report of eight years ago.