GB790146A - An improved method for the production of photographic contour maps - Google Patents

Abstract

790,146. Producing maps photographically; photograph enlargers. MAHAN, R. O., and TOWILL, R. M. Sept. 23, 1955, No. 27245/55. Classes 98(1) and 98(2) A contour map is produced photographically from a series of stereoscopic aerial photographs by making diapositives of the photographs, setting the diapositives up in a stereo-projector and plotting contours on a semi-transparent compilation sheet by known methods, forming a transparent positive of the compilation sheet and covering it with a mask, removing the mask from the positive between selected contour lines and projecting through the unmasked area on to a sensitive film a restituted image of that area from the corresponding diapositive, the image being enlarged to an amount depending on the mean contour height of the unmasked area, remasking the positive and repeating the unmasking and projecting steps for areas between all the selected contours in turn, developing the film and producing a map therefrom which will show the contour lines and a restituted photograph of the area corrected for the varying heights. The diapositives may be set up in a plotter and the contours plotted as described in U.S.A. Specification 2,492,870. The compilation sheet so produced is inked in, together with any names and other information required on the finished map and a high contrast negative produced from which the positive film is made. The positive film is masked all over with red masking tape, placed on a light table so that the contours are visible through the tape, and the tape is then cut along the selected contour lines with a sharp knife. The mask is removed between a pair of contour cuts and the partially masked film is placed over a light sensitive film on the table 10 of the restitutional enlarger shown in Fig. 1, and the corresponding diapositive 32 is placed on the projector 12 and illuminated from light box 29. The projector 12 may be adjusted by knobs 30 to have the same tilt as in the stereo plotter. The enlargement is adjusted dependant on the mean contour height to give a true scale of reproduction. The table 10 is vertically adjustable on the screwed rods 14 by rotating a hand wheel 21 and the films are held on the table by suction from a pump 36 and pipe 35. After exposure, the masked film is removed and the unmasked area blacked out; the next masking strip is then removed and the process repeated. The exposed film is then developed to give the final negative from which the map is made.