History and Development of Instruments and Apparatus for Air Photography (Especially for GATE-Geospatial 2022)

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From the end of the Great War period onwards, efforts were being made to provide instruments which would stabilize the aircraft and camera and enable determination of the position in space at exposure to be arrived at with a minimum of ground control.

Daumier Honoré | Nadar Élevant La Photographie À La Hauteur …

McKinley considered that 3° was a “slight” tilt and expressed the opinion that a good photographic pilot should be able to fly strips twenty-five to thirty-five miles long with an altitude variation not greater than a hundred feet.

Many of the early efforts were with gyroscopic forms of control, either of camera or aircraft. Very little success was met with for a number of years, though instruments for indicating turning and tilt were developed. The ordinary altimeter, which records on the photograph, is very approximate, and the statoscope (or differential aneroid) enables heights to be recorded fairly accurately with reference to a particular flying height. Aneroid tables and details of a standard aneroid and corrections to be applied have been published by the War Office.

For a number of years, it has been possible to project accurately through lenses of a limited field, but photographic surveying inaccuracies arose chiefly because of displacements of the image between exposure and final printing, due largely to distortions of film and paper. Recent improvements in the production of film bases and papers with very little distortion have made it generally possible to fix the position of the image within a plottable error. It is now also possible to produce an accurate photograph over a much wider angle of lens than formerly, the distortions being quite small in such lenses as the new Ross Wide-angle, and the Zeiss Topogon.

Some of the original experiments made by the Royal Air Force using the “Three-axis Automatic Control,” show that “stabilized flight is now no figure of the imagination as it was in 1923; level flying has become a mechanical possibility, to the immense advantage of air survey.”

It was stated in 1935 that Royal Air Force policy did not provide for routine air survey photography. ′ It is considered that routine work should generally be carried out by Civilian Firms … It is the intention of the Air Staff, to keep available trained personnel from which a survey unit can be formed at reasonable notice. ″ In Canada, however, much flying for Air Survey photography has been carried out by the Royal Canadian Air Force. The Departmental Committee on the Ordnance Survey has recommended the formation as soon as possible of a special Survey Unit capable of satisfying the requirements of the Ordnance Survey, and the Aircraft Operating Company as mentioned on page 5 is going ahead with this project.

The satisfactory development of the automatic pilot has completely changed the position. Flying “is so superior to that of the piloted aircraft for survey purposes, that it would seem most undesirable nowadays to attempt any air survey photography without its assistance.”

Major. D. R. Crone, R. E. , has shown that flying straight and level in taking obliques has enabled a reliable levelling method to be devised. This method he has used with success, particularly in the Himalayas.

The present position is that the aircraft can be set on a course and fly straight with a tilt of the order of 1°. It has been a tendency of the automatic pilot to fly with a slight bias probably due to some unbalanced gyroscopic force, and experiments on a method of navigation depending on tuning in to a broadcast wireless station have been carried out by Captain Charles Lloyd who claims to have reduced this effect. The successful introduction of the automatic pilot has widened the field of survey very considerably instruments such as the Aldis Camera Sight and the Course and Distance Calculator have made it much easier for the pilot to fly the area and ensure that it is all covered with the requisite overlaps.

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