Patent GB-748863-A (GB)
Title: A method of terrestrial photogrammetry
IPC: G01C11/06
Filed: 1951-12-20
Abstract: 748,863. Photogrammetry. POIVILLIERS, G. J. Dec. 20, 1951 [Dec. 20, 1950; Dec. 10, 1951], No. 29936/51. Classes 97 (2) and 98 (1), In a method of terrestial photogrammetry, one or more datum markers is or are each successively located at known heights above points on the ground, the positions of which are to be determined and lie within a field common to two or more photographic cameras, and the successive locations of the marker or markers are recorded on a single sheet of photographic material in each camera. The method is specially applicable to surveying from the ground terrain in which details are hidden by rising ground, vegetation or the like. In one form of the method, when the cameras have been set up, a datum staff is taken to a chosen point invisible from the cameras, though the top of the staff, on which a lamp is carried, lies in the field covered by both cameras. The camera shutters are released simultaneously, e.g. electrically. The staff is then moved to further points, at each of which photographs are taken simultaneously on the same photographic plate or film. Since the lamps are brighter than surrounding objects, the images thereof are not blotted out by the image of the terrain. As shown in Fig. 3, the datum staff consists of a light rigid rod 7 supporting an electric lamp 1 which illuminates a cross- or T-shaped slot. Conductors in the rod and a switch Z enable the lamp to be lit by means of a battery carried by the operator. The rod rests on the ground by base 5, and has handles 4 for holding it in the upright position indicated by a level 3. The shaft may be made of a number of interfitting sections with mechanical and electrical joints, and the lower part is telescopic to allow small variations of height. In another form of the method, a camera is used in which the field of view is restricted by an adjustable diaphragm to a small area around the staff. As shown in Fig. 4, the camera 51 is supported on a tripod 10 and levelled by levelling screws 11 and levels 12, 12<SP>1</SP>. A telescope 13 is mounted on the camera to pivot about the axis of the objective lens O. The cameras are lined up by laying the telescopes 13 of each pair on each other. The field of view is restricted by a tube 53 movable by a ball-and-socket joint about the objective. The tube has a bead sight 57 which, with a mirror 58 carrying a backsight 9, enables the tube to be laid on the staff. When the shutter is actuated the staff is photographed but the surrounding terrain is excluded. In another form of camera, a movable tube is mounted inside the camera and coupled to levers carrying sights outside the camera. In a further form of the camera, roller blinds with slots at rightangles are positioned just in front of the plate or film and are coupled to sighting means. After recording the position of the marker or markers, the whole field of the objective is used to record the terrain. For hydrographic work the markers are carried in boats at a fixed height, the depth being read on a sounding line. The positions of the markers are transferred to maps from the photographs by the usual methods.