Patent GB-276795-A (GB)
Title: Improvements in or relating to photographic surveying
IPC: G01C11/00
Filed: 1926-07-19
Abstract: 276,795. Fourcade, H. G. July 19, 1926. Stereogrammetric apparatus.-Relates to apparatus for determining the position in space of points shown on a pair of aerial photographs, taken from two different points of view, and for tracing on a plane surface a map of the surface represented. Two photogoniometers A hold photographs a<1>, obtained as results of exposure in aeroplane cameras, and are mounted on a frame b<1> in such a manner that each can be turned separately around a common axis of rotation, determined by horizontal pivots c<1>, and round axes at right angles to this axis, parallel to the plates a<1> and determined by pivots d<1>. Each plate a<1> can be rotated in its own plane. The axes all pass through the front nodal point of the lens f<1> of its photogoniometer. Light rays from the plates a' are reflected from mirrors k<1>, j<1> into a fixed binocular telescope y<1>, provided with sighting marks and enable the photogoniometers A to be adjusted until a correct stereoscopic image is formed. The relative position of the plates a' is then fixed. The mirrors k<1>, j<1> are mounted on slides i<1> carried on guides h' and may be moved parallel to the axis determined by the pivots c<1>, thus traversing the stereoscopic image across the field of view, while movement in the other direction is effected by swinging the photogoniometers A round the pivots c<1>. The mirrors j<1> are fixed on the slides i<1> and the mirrors k<1> are actuated by a sector t' on a rod o<1> connected to a sector s<1> of double radius so that they move through half the angular displacement of the slide with respect to the lens f<1>, ensuring correct observation. The mapping system comprises a carrier b<2> fitted with a pencil m<2>, moving over the surface of a drawing-board n<2>. Two rods o<2> connect the carrier to the photogoniometers and are arranged so that they can swing as in one place about an axis parallel to the axis of the pivots c<1>, the rods o<2> diverging and passing through sleeves q<2>, r<2> pivoted on a transverse member s<2>, movable by pivots t<2>. The sleeve r<2> is adjustable in a slot v<4> in the member s<2> These rods o<2> also pass through sleeves e<3>, g<3> mounted on slides w<2>, x<2> which are connected by cross-bars c<3>, d3 and rods a<3>, b<3> to the mirror slides i'. Having set the plates a<1> and the photogoniometers A in correspondence for stereoscopic vision, the length of the base is set off to the scale of the desired map by sliding the block v<2> carrying the sleeve r<2> to the appropriate positions in the slot v'. The left-hand mapping rod is made vertical when the line of collimation of the left hand telescope is perpendicular to the axis of the pivots c' and the rods a' are clamped to the corresponding slide i<1>. The right hand rod o<2> is then similarly set and then both rods o<2> are set in a vertical plane and the photogoniometers A are rotated together by the screw h<2> until the reading on the arc i<2> corresponds with the rotation necessary to bring a trace on the photographs of the vertical plane into the horizontal measuring plane of the apparatus. Contour lines may now be drawn at heights indicated by the scale u<4>, by moving the pencil carrier l<2> so that the sighting marks in the telescope are kept in apparent contact with the features to be mapped. A cutting tool may be substituted for the pencil to produce a solid model.