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information correctly interpreted requires a knowledge of Photo Interpreta-
tion. I have seen times when the Photogrammetrist preparing a map was at a
loss to analyze some of the information on the photography used to compile
the map. Then time may be lost field checking or contacting a PI man. A
knowledge of Photo Interpretation could have given the Photogrammetrist
the solution to his problem.
So the Photo Interpreter and Photogrammetrist can be of assistance to
each other in many ways. But they must understand the problems and ob-
Jectives of one another. Often time is of an essence to the PI man and he
must use shortcut methods, approximate procedures, or *horseback methods".
These are often frowned upon by the Photogrammetrist because the end result
is not of the accuracy usually employed by the Photogrammetrist.
These *horseback methods" which are at times employed by the Photo
Interpreter may seem to be inaccurate because the accuracy of the final
product is not the ultimate that could be obtained with more time and
equipment available. But often pin-point accuracy is not required and under
such circumstances I do not see the necessity of spending time and money to
obtain it. The intelligent procedure is to evaluate the request, determine the
accuracy required and prepare the results accordingly.
In certain applications of Photo Interpretation, "stratification", or the
delineation of homogeneous units such as tree, species, waterfowl densities,
grass types etc, is of importance. Accuracy within 5% or 10% may be all
that is required. If this information is taken by the Photogrammetrist, trans-
ferred by use of a $50,000 plotting instrument with a high degree of accuracy,
time and money may have been lost, and unnecessary accuracy strived for.
What the Photo Interpreter is often looking for is an instrument that will
transfer this information to a base sheet with a fair degree of accuracy; an
instrument that is not too complex in operation, is portable, easy to set-up,
and does not require ground control and other detailed information for its
operation. There are some such instruments on the market today but I think
there is room for more.
Do not misinterpret my remarks. I am not suggesting that the Photo
Interpreters run out and obtain 10 cent lenses and make their own stereo-
scopes, nor that the highly accurate and efficient plotting and measuring in-
struments now in use should never be employed by the Photo Interpreter.
Any improvements that can be made in stereoscopes, mechanically, opti-
cally, or otherwise will always be greatfully received by the Photo Interpreter
for such will help make his work easier, faster and more efficient. There are
many times when accuracy is of prime importance — the foremost factor —
and should be obtained to the highest possible degree. If it is measuring the
width of a bridge to determine whether the tanks advancing with your ar-
mored unit can squeeze across — you do not want to know just to within a
foot or two. In a measurement as critical as this a few inches may make the
difference between success and failure. Hence you want to know the measure-
ment as accurately as it is possible to determine. The determination of fields of
fire, defilade areas, and visibility from an observation point all should be
determined with a high degree of accuracy. The depth of water over a reef at
time of landing can be a key factor in the succes or failure of a landing oper-
ation and must not be approximated.
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