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Aviation History
1950
1950 - 0715.PDF
FLIGHT, 13 April 1950 463 THE WORLD IN CAMERA Modern. Techniques of Air Survey : An Explanation for the Layman By JOHN YOXALL To assist in the compilation of this article, Hunting Aerosurveys, Ltd., put at our disposal many examples of the work executed by themselves and their associated Commonwealth companies. At their Boreham Wood head- quarters we have been invited to see and photograph in action typical apparatus used in modern photogrammetry. The air-survey companies of the Hunting Group grew from the first commercial air-photographic concern ever formed (Aerofilms, Ltd.) and from these early specialists in oblique photography has grown the present large organ- ization. Some details of the companies concerned, and of their various activities, are recorded. THE early history of air-to-ground photography in thiscountry might, perhaps, be described as typicallyBritish. Although offering such obvious possibilities, the scip"f~e was left to private individuals to develop. From the late 1860s, when the technique of photography became generally known, attempts were made to obtain air pictures by means of cameras attached to kites and, despite the comparatively long exposures required, quite reasonable results were obtained from the baskets of balloons. In the Air Battalion of the Royal Engineers, and the Royal Flying Corps in its first two years, the need for photo- graphic reconnaissance was felt; odd photographs were taken by the officers with their own cameras, but little official interest was shown until the beginning of the 1914-18 war. The first air camera designed specifically as such was the A type made by Thornton Pickard, Ltd., in the best brass-bound and mahogany style of construction of that period. Of truncated rectangular cone form, it was hung on the outside of the fuselage and fed by the pilot with single plates in fabric and celluloid sheaths. In 1915 came the first automatic air camera, the Fi, made by Williamsons, a firm whose name has been associated with all the successful automatic cameras used in the R.A.F. ever since that date, and who to-day produce the new O.S.C. Mk IT, which is considered to be the standard air-survey camera. The early automatic cameras all used plates, but after A Bristol 170, with interior specially adapted for air-survey photo- graphy. It is in use with Hunting Aerosurvey's expedition in Iran. This photo-diagrammatic illustration shows how coverage of an area is obtained. A 60 per cent longitudinal and a 30 per cent latitu- dinal overlap are required. The aircraft is the Percival Survey Prince. the 1914-18 war a change was made to roll film. Curiously enough, there is a tendency to-day to return to the use of plates for very accurate work, because slight inaccuracies are still caused by the stretching and contraction of film as it is wetted and dried in processing. Air survey in its early stages suffered somewhat from the fact that enthusiastic friends claimed more for it than it was able to deliver; and, although it was obvious that at some future time it would replace the tedious ground survey methods previously used, the degree of accuracy attainable at the time did not compare favourably with that of the orthodox method. To-day, with the many aids available, the degree of accuracy is extremely high. An outstanding example of present-day accuracy is the 1/480 (40ft to iin) survey done by Hunting Aerosurveys for British Railways. Employing photogrammetric measurement almost entirely. Two Austers and a Percival Proctor, used for " obliques." When Aerofilms, Ltd., suited, 31 years ago, they were using D.H.9s»
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