Patent GB-553299-A (GB)
Title: Improvements in and relating to maps and the production thereof
IPC: G01C11/00
Filed: 1941-04-07
Abstract: 553,299. Photographic production of maps. AERO SURVEY CORPORATION. April 7, 1941, No. 4636. Convention date, April 6, 1940. [Class 98 (ii)] [Also in Group XV] A photographic plan of terrain substantially correct to scale is prepared by making a scale model of the terrain, temporarily projecting in registry thereon a photograph of the terrain taken from aircraft, and taking a photograph of the model with the projection thereon, using only rays which leave the model in a direction normal or substantially normal to its datum plane. A set of photographs so made, of adjacent areas of terrain, may be assembled in registered juxtaposition so as to build up a correct mosaic of the entire terrain to be represented. Other photographs may be taken of the model with the temporary projection thereon, as seen from positions giving oblique views, in order to assist in identifying the terrain when viewed from such positions. The model may be produced in known way by projecting a pair of photographs of the terrain, taken from adjacent view-points above it, upon a carvable block so as to produce a plastic image of the terrain on the block, and carving the block to coincide with the plastic image. Contour markings may be superimposed on the photographic plan in any way, and in particular by using for making the model the method set forth in Specification 530,331 employing a carvable laminated block. From the photographic plan a scale map may be produced showing both photographic features and topographic indicia. Figs. 2 and 3 illustrate one form of apparatus for carrying out the method. It comprises a base 11 supporting a carvable block 3, a pair of universally-adjustable projectors 1, 2, a framework 6, 7 provided with rails 9, 10 along which an inclined mirror 5 may be laterally displaced in its own plane from the position shown in Fig. 3 determined by a stop 12, to the right into a position determined by a stop 13. Each projector field fully covers the block 3. In each of its positions, the mirror reflects slightly more than half the area of the block 3 to a telephoto camera 14 mounted on a stand 17, the two views being in overlapping register at their inner contiuous edges. In front of the focal plane of the camera 14 there may be disposed a slide 18 having an aperture which permits the two reflected half-images corresponding to the two positions of the mirror to be photographed in succession; and provision may also be made in the slide for photographing the block in four exposures, one quarter of the area at each. The slide 18 may be replaced either by an angularly adjustable stop in the camera, provided with a semicircular aperture, or by an opaque masking plate hinged to the mirror stand, the plate being adjustable through 180 degrees to mask whichever area of the stand is not occupied by the mirror. In use, for producing a map showing both photographic a topographical detail, the mirror 5 is first removed entirely, and two overlapping diapositives of the terrain taken from a high altitude, are placed in the projectors 1, 2 so -as to project a plastic image of the terrain onto the carvable block 3. Red and blue filters may be used in known manner in the projectors, and red and blue spectacles in viewing the plastic image. The block 3 may be laminated as described in Specification 530,331 to yield contour markings. It may, for example, be formed of alternately coloured layers, e.g. blue and white ; or of alternate grey and white layers; or of white layers separated by thin films of black, grey, or coloured material ; or all its layers may be of normally white material, alternate layers being impregnated with a chemical indicator, e.g. phenolphthalein, so that the zones or lines may be made to appear or disappear at will by treatment with alkaline or acid solutions. The block is carved to fit the plastic image, and three widely-separated registration marks are made on its surface. This block 3, or a block produced from it as by moulding, is then photographed, while the plastic image is still projected on it, by the camera 14, in two or four successive exposures as indicated above. The red and blue filters are removed from the projectors when making these exposures, and if desired a colour filter is placed over the lens of the camera 14, its colour being chosen so that it will either allow or prevent the recording of the contour markings when a laminated block 3 is used. The resulting photograph is developed as a negative, and exhibits all the photographic details of the terrain in substantially correct planimetric relationship, and maybe also contour markings. An image of this correct negative is projected upon drawing paper, and with the help of the image the topography of the area is filled in in ink on the paper, and the positions of the grid lines and the three registration marks on the image are also recorded in ink thereon. This paper record is then copied from the position just occupied by the negative when it was being projected upon the paper, and from the resulting negative a diapositive showing the topographical details is printed, or made by reversal. The corrected negative of the terrain, made in the camera 14, is then bound up in registered superimposition with the topographical diapositive, a normal image is projected from the combination, and a normally-developed photograph of this image is made, thus yielding the finished map of the particular area of terrain concerned. U.S.A. Specification 1,980,981, which describes a similar method in which the projected image is permanently recorded on the scale model by photographic means, is referred to.