Patent GB-329383-A (GB)
Title: Improvements relating to apparatus for use in connection with photographic aerial surveys
IPC: G03B27/68
Filed: 1929-02-19
Abstract: 329,383. Aldis, A. C. W. Feb. 19, 1929. Photographic surveying.-Relates to means for correcting photographs of the ground taken from an aircraft in order to remove the distortion due to inclination of the axis of the camera to the vertical and thus to render the photographs suitable for the production of a map therefrom. The apparatus can also be used for determining the said inclination. The photograph is mounted in an optical-projection apparatus, the light from which is received by a camera in which the corrected photograph is to be taken. The axis of the projection apparatus is angularly adjustable relatively to that of the camera and in order to enable it'to be correctly set there is interposed between the camera and the photograph a screen on which is marked a quadrilateral corresponding to that joining four points on the ground of which the images appear in the photograph, the exact positions of these points having been determined by ground survey. There is also marked on the screen a number of closely spaced lines parallel to each of the sides of the quadrilateral. A quadrilateral joining the images of the same four points is also drawn on the photograph and the projector is then adjusted relatively to the camera and screen until, as seen from the nodal point of the camera lens which is made to correspond to the view point of the camera by which the photographs were taken, each side of the quadrilateral on the photograph coincides with, or is parallel to, one of the corresponding lines on the screen. When the ground concerned is substantially flat only one screen as above described is needed; but if the four chosen points have substantially differing altitudes the quadrilateral joining them does not lie in one plane, and in this case two screens may be used, the plane of one corresponding to that containing two adjacent sides of the quadrilateral, and the plane of the other to that containing the other two sides. In the form shown the camera c and screen holder hare mounted on guides b on a base a and the camera lens d is carried by a bracket e secured in any convenient position to the base. On the bracket vertically below the view point of the lens d is a pivot f on which is mounted a frame carrying the cylindrical projector g and comprising end members i, j and guides k, l. The projector is supported on rollers m one of which is engaged by a friction wheel n on a rod o to enable the projector to be turned about its axis. The projector can also be moved longitudinally with the rollers along the guides k, l. The part of the photograph to be projected is supported on a plate r which may bear a reference mark to which a datum mark on the photograph is adjusted to obtain proper centring of the photograph. The holder h, containing one or more screens x marked as above described, is also of cylindrical form and is supported by rollers s on a bracket t adjustable on the guides b, one of the rollers being adapted to be rotated by gearing from a rod v for adjusting the holder about its axis. For making the required adjustment of the projector and screen holder the camera lens d is replaced on the bracket e by a viewing instrument, Fig. 1<a> which virtually transfers the observer's eye to the view point of the lens. The lines on the photograph are then brought into apparent parallelism with those on the screen by adjusting the projector and screen holder about their axes and by rotation of the projector about the pivot f. The projector is then in the proper position for producing a corrected photograph in the camera. When two screens are used, the holder h is made in two relatively rotatable parts, each carrying one of the screens. In a modification the projector is not capable of adjustment about its axis, but is so mounted that its axis can be swung about the view point in either of two planes at right-angles to each other. The angle of tilt of the camera used in taking the photograph may be obtained from the abovedescribed adjustments.