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AERIAL PHOTOGRAPHY BY THE GROUPE DES ESCADRILLES
PHOTOGRAPHIQUES BELONGING TO THE INSTITUT
GEOGRAPHIQUE NATIONAL
by
J. Cruset, Ingénieur Géographe Institut Géographique National, France.
The Institut Géographique National (French National Geographical In
stitute) is one of the few existing geographical departments with its own photo
graphic facilities. A variety of factors dictated that specially trained squadrons
should be placed at the disposal of the Department responsible for photo-
grammetric surveys: the need of aircraft suitable for the work in hand, the
diversity of this work, the vast area covered by the territories which form the
Union Française, and the importance for the quality of the results of having
specialized and highly-trained aircrews. These aircrews now form an essential
part of the I.G.N.
The Groupe des Escadrilles Photographiques, or G.EP. (Photographie
Group) consists of 4 squadrons:
1 —Squadron of 4 twin-engined NC. 701’s employed principally in France
on high-precision surveys;
2 — 5 powerful twin-engined LeO 455’s employed in France for high-
precision surveys of mountainous ground, in North Africa and also for certain
tasks in Western and Central Africa;
3 — 3 twin-engined LeO 453’s with a lower ceiling than the 455’s nor
mally employed in North Africa and recently in Indo-China;
4 — 4 four-engined B.17’s converted for photographic service and nor
mally employed in the overseas territories of the Union Française.
All these aircraft have a navigator’s cabin with excellent visibility and a
photographic cabin which is more or less identical on all types of aircraft.
The cameras in use are:
For high-precision surveys — Poivilliers-S.O.M. automatic, 192 plates 13 X 18,
or 96 plates 19 X 19;
For smaller-scale surveys — S.O.M. automatic cameras for 19 cm wide film.
The focal length in common use is 125 mm.
Various components are fitted as equipment to the aircraft and remain as
such, viz: the intervallometer fitted with a sight which automatically allows
for speed and drift, the universal (i.e., capable of receiving all types of S.O.M.
cameras) and panoramic mounts, and the current transformer-regulator.
The present strength of the Group is 112, 49 aircrew and 63 others.
Flying techniques have been most carefully worked out. Naturally they
differ according to whether good-quality cartographic material is already
available or not. The accuracy of the navigation is remarkable; there is abso
lutely no need to have recourse to radio-aids, which are extremely expensive and
would, in any case, be extremely difficult to install over the vast areas to be
covered in Africa.
The Group can cover over 500,000 sq. m. a year.
