G VI 1-30 
PHOTOGRAMMETRIC ENGINEERING 
information on this subject published during the reporting period, it is sum 
marized briefly below. It will be noted that while there are differences in the 
two lists, these are not major ones. 
R. F. Thurrell (1943) 
Scale: Vertical, 1:20,000. Obliques desirable as supplementary source 
materials. 
Size: 9 or 10 inch square photographs represent answer to the oppos 
ing requirements of economy of photography, and ease of 
handling. 
Focal length: 8jj" best from point of view of stereo-exaggeration provided at 
50% overlap. 
Overlap: 50% normal. Increase as necessary for special problems (6" 
focal length at 80% will provide both high exaggeration and 
low exaggeration stereo pairs of the target area. 
Color: Highly desirable, but usually not practicable due to cost and 
difficulty of handling. 
Other: Early spring and late fall best seasons due to lack of vegetation 
camouflage. No snow cover. Cloud cover less than 10%. 
F. A. Melton (1943) 
Scale: Vertical normally 1:20,000. 
Size: 7 by 9 inch prints preferred to 9 inch square or larger, because 
of ease of handling and less stereo distortion at edges. 
Focal length: 12" preferred to shorter focal lengths due to flatter field of view 
in stereo model. 
Overlap: 65% to 70%, with side lap of 20% to 25%. 
Color: Highly desirable but usually not practicable due to cost and 
difficulty of handling. 
Other: Photographs should not be indiscriminately “dogged” in print 
ing, since significant tonal changes on the ground may be min 
imized. 
Bibliography 
Belcher, D. J., (1953), “Terrain Intelligence and the Future of Mineral Prospecting,” Selected 
Papers on Photogeology and Photo Interpretation, (April), GG 209/1. United States. 
Benninghoff, W. S., (1953), “Use of Aerial Photographs for Terrain Interpretation Based on Field 
Mapping,” Photogrammetric Engineering, (June), pp. 487-490. United States. 
Black, R. F., (1952), “Polygonal Patterns and Ground Conditions from Aerial Photographs,” 
Photogrammetric Engineering, Vol. 18, p. 123-134. United States. 
Brasseur, R., Flandrin, J., (1955), “Photogeology and its Use,” French Petrol Institute, (May). 
France. 
Blanchet, P. H., (1955), “Photogeologic Exploration by Multiplex,” Journal of the Alberta Society 
of Petroleum Geologists, Alberta, Canada, (March). 
Colwell, R. N., (1953), “Aerial Photographic Interpretation of Vegetation As An Aid to the Esti 
mation of Terrain Conditions,” Selected Papers on Photogeology and Photo Interpretation, 
(April), GG 209/1, United States. 
Fisher, W. A., (1953), “Photogeologic Studies of Arctic Alaska and Other Areas,” Selected Papers 
on Photogeology and Photo Interpretation, (April), GG 209/1. United States. 
Fisher, W. A., (1955), “Photogeologic Instruments Used by the U. S. Geological Survey,” Photo 
grammetric Engineering, (March), Vol. XXI No. 1. 
, (1955), “French Air Forces No. 105 (Aviation and Geology),” French Air Ministry, (June), 
France. 
Gandillot, J., (1952), “Geography No. 9 (The Airplane, Geologist’s Eye),” French Geological So 
ciety. France. 
Gandillot, J., (1954), “B.S.G.F. Col. 1-3. 1-4. (Aerial Photographs in Geological Research),” 
French Geological Society, (Nov.). France.