Patent GB-319867-A (GB)
Title: Method and apparatus for aerial survey
IPC: G01C11/00
Filed: 1928-07-23
Abstract: 319,867. Georgiadis, G. B. July 23, 1928. Photographic surveying-apparatus.-Relates to apparatus mounted on aircraft for taking photographs of the ground, from which maps are to be produced, and comprises means for determining (a) the tilt of the axis of the camera at the moment of taking an exposure and (b) the differences between the altitudes of points on the ground which appear on the photograph, in order that corrections may be applied for these factors. To determine the first factor there is associated with the camera 1, 2, Fig. 1, by which the ground photographs are taken, a second camera 5, 6 having its axis parallel to that of the first camera, and arranged so that the plates of both cameras are exposed simultaneously. The second camera is arranged to take photographs of a cardan system comprising an outer ring 11 rigidly connected to the camera with its plane parallel to that of the plate 6, and supporting by pivots 12, 13 the ring 14 which is provided with pivots 15, 16 supporting the frame 17 which carries a compass 18 or a gyroscope. The frames 14, 17 are provided with pairs of upwardly-extending pins 21, 22 and 23, 24 situated on the respective pivot axes. The axes 12, 13 and 15, 16 are respectively parallel to the transverse and longitudinal axes of the aircraft. Thus if the aircraft is tilted about the axis 12, 13 the frame 11 appears in the photograph as a circle and the frames 14, 17 as similar ellipses, and for a tilt about the axis 15, 16 the frames 11, 14 appear as circles and the frame 17 as an ellipse. The pins 21 - - 24 facilitate the determination of the tilt by the variations in the lengths of their images on the photograph. The frame 35, Fig. 4, carrying the cameras may itself be suspended from a gimbal system 26 - - 33 and a spring 36 may be provided to absorb shocks: the gimbal system may be provided with one or more gyroscopes. The angle of tilt can be determined by reprojecting the image on the plate 6, by an apparatus similar to the camera, on, to a screen which can be adjusted so that the images of all' the cardan frames appear thereon as circles. Fig. 8 shows a simple form of such apparatus in which the screen 47 is mounted on pivots 46 in a stand 44 parallel to the plate 6; a pointer 48 secured to one of the pivots cooperates with a fixed protractor scale 49. Figs. 9 and 10 show a complete form of the re-projection apparatus permitting all necessary adjustments of the photograph and screen. A circular base 51 supports hollow uprights 53 in which are mounted rods 55 with screw-threaded upper parts 56 connected by a hollow frame 58 within which are mounted the supports for the projection apparatus. By suitable gearing the frame 58 can be adjusted vertically by a handwheel 70 and the projection apparatus can be adjusted within the frame by a handwheel 71. The base 51 is provided with bearings 83, 84 for a screwed shaft 85 operated by a wheel 86 and engaging an internal thread in the base 87 of the support on which the screen is mounted. The base 87 carries supports 90 and a guide 91 for a rotatable circular frame 92 carrying a pillar 93 having an internal thread engaged by a screw-threaded projection 97 from a box 95, which is also provided with projections 96 engaging in guides 94 on the supports 90. The box 95 can thus be raised or lowered by turning the frame 92. The projection screen 104 carried by the box 95 is hinged to two toothed circular frames 101, 103 at rightangles to each other and adjustable by worms 100, 102. To enable the photographs to be corrected for differences in elevation in the ground covered, there are marked on the ground a number of circular figures A - - H, Fig. 12, of known diameters, these figures being either circles marked on the ground e.g. A, B or circles, such as G, simply defined by a number of stakes of known length driven into the ground, with a further stake at the centre of the circle. When the photograph including these figures has been corrected as above described to compensate for the tilt of the axis of the camera the differences in level existing on the ground can be deduced from a micrometric measurement of the diameters of the images of the several circles. As an alternative method of determining these differences of altitude the single camera on the aircraft for photographing the ground can be replaced by three cameras 129, 130, 131, Fig. 21, the axis of the camera 130 being vertical and those of the cameras 129, 131 being equally inclined to the vertical in opposite directions. With such an arrangement a point X2 which is photographed in one position of the aeroplane by the camera 129 will be photographed in a succeeding position by the camera 130; a point X<1> will be successively photographed by the cameras 130, 131, and so on. The photographs so obtained are utilized in a projection apparatus, illustrated diagrammatically in Fig. 22 but fully described in the Specification, comprising three suitably positioned and adjustably mounted instruments 132, 133, 134 carrying groups of projectors 129, 130, 131 corresponding to the camera arrangement of Fig. 21. Screens 135 a, b and c adjustable horizontally and vertically are associated with the projectors. Assuming that the tilt correction has already been applied, the screens are adjusted until, for example, the images of the point X1 from one projector 130 and one projector 131 coincide on the screen 135<a>. The necessary vertical adjustment of the screen is then a measure of the altitude of the point X1.