WORKING GROUP 1
WELANDER
37
photographs above in the scale of 1 : 10,000, containing a settlement, was
used. On a lawn, the limit between the shadow of a house and the adjacent
sunlit area was measured with a micro-photometer. Further, the limit
between a sunlit roof and the adjacent shadow was analysed. The cor
responding T-function is shown in fig. 9. As a control, a bright test line was
also laid out before photography. The dotted curve is the function for this test
line. The agreement between the T-functions as calculated from the natural
test pattern and from the painted test line is satisfactory. This means that
there are certain possibilities for determining T-functions of aerial photographs
without using special test patterns.
Conclusions
The methods and investigations reported here show that the transfer
functions are already a valuable aid in determining the quality of aerial photo
graphs. However, an essential step remains, viz. the investigations of the cor
relation between the quality, as measured above, and the results of photo
interpretation and parallax measurements, expressed as standard deviations.
Such an investigation is being planned.
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