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nen wird gegeben auf 
Experimentelle Ergeb- 
FACTORS AFFECTING THE INTERPRETABILITY OF 
AIR PHOTOS” 
by K. B. Jackson, B.A.Sc., D.Sc., 
Professor of Applied Physics, University of Toronto 
Abstract 
This article discusses the qualities of photographs best suited to the 
needs of the photo-interpreter and the photogrammetrist and suggests 
means of achieving them and methods of abstracting the information such 
photographs contain. 
A description is given of the targets that have been constructed to 
test the walidity of the proposals in actual aerial photography at scales 
between 1:2400 and 1:15840. 
Introduction 
This paper is an interim report on work that has been in progress at the University 
of Toronto for some years. It was initially sponsored by the Research Council of 
Ontario, but during the past three years it has been supported by the Ontario Depart- 
ment of Lands and Forests for the more specific purpose of determining the best 
equipment, material and procedures to be used in the current re-photography of Ontario. 
Photo-Interpretation—Two Kinds 
There are two kinds of photo-interpretation: that practised by the traditional 
photo-interpreter, be he forester, geologist, highway engineer or town planner, and 
that by the photogrammetrist. The first, the traditional, is interested in identifying 
the things he sees and also in obtaining an overall view of the terrain. He requires the 
means to make intensive and extensive examinations of the detail and area involved. 
The photogrammetrist, on the other hand, wishes to locate what he sees. The 
accuracy of the measured co-ordinates of specific points in several photographs is of 
the first importance to him. 
Both interpreters will require the best possible rendering of detail, but the first 
may also require a more “natural” degree of tone-rendering than the second, and a more 
“natural” rendering of the third dimension may prove to be a real advantage. 
Factors Affecting Interpretability—Two Groups 
The information available from a stereo pair of photographs will depend on how 
they were made—information input—and how they are looked at—information extrac- 
tion. 
There are, therefore, two very different groups of factors that affect the ultimate 
interpretability of a pair of photographs: those affecting the quality of the photographs, 
and those affecting the observer’s ability to see what they contain—visual aids. 
(The ability and experience of the interpreter is of course the over-riding factor, 
but iz will be taken for granted in the present discussion). 
*An amplification of a paper presented at the Annual Meeting of the Canadian Institute of Surveying, 
Ottawa, January 29, 1959 and published in The Canadian Surveyor, Vol. XIV, No. 10, ( October, 1959), 
pp. 454-464.