Patent GB-430995-A (GB)
Title: A device for producing by purely photographic means a topographic plan
IPC: G01C11/00
Filed: 1934-01-02
Abstract: 430,995. Photogrammetry. AEROTOPOGRAPHIE, 75, Boulevard de la Mission Marchand, Courbevoie, Seine, France. Jan. 2, 1934, No. 163. Convention date, Jan. 25, 1933. [Class 97 (ii)] For making by photography a topographic plan from a plate carrying a photographic record of the ground, an adjustably mounted projecting chamber supporting the plate projects an image adapted to be recorded in a series of bands on a base plate covered with a light sensitive sheet. A screen having a slit and mounted adjacent the base plate is given successive displacements in a determined direction, the slit having the shape of a deformable parallelogram whose opposite sides parallel to the direction of displacement of the slit have a length proportional to the speed of displacement and are at a constant distance apart for each recorded band. The slit is displaced in the mean direction of the lines of maximum slope with the sides of the slit not parallel to the direction of displacement maintained parallel to the level lines, as indicated for example on a separately prepared contour diagram, and the distance between the projecting chamber and the base plate is adjusted according to the altitudes of the points of the ground being recorded through the slit. In one form, a projecting chamber, carrying a plate, is supported in a frame over a flat board 8 in a position corresponding to the position of the camera relative to the ground when the plate was taken. Immediately above the board 8 is a carriage 4 carrying a plate 9 in which is arranged the slit 10. The carriage 4 may be displaced along the rails 5 by a screw 11, and the rails 5 along a pair of rails 7 at right angles by a screw 13. The supporting disc 24 for the slit 10 is turned until the shorter sides of the slit are parallel to the mean slope of the ground being reproduced, as indicated on a separately prepared contour diagram, and the carriage 4 is displaced over the board 8 in this direction of mean slope by suitably gearing together the screws 11 and 13. The contour diagram is mounted on a drum 25 whose rotations are proportional to those of the screw 13 and a carriage 28 is mounted to slide parallel to the axis of the drum, and is moved by a screw 26 geared to the screw 11. A ruler 30 pivoted at the end of a pointer 29 on the carriage 28 is connected by gearing to the members forming the longer sides of the slit so that by maintaining the ruler 30 parallel to the contour lines the operator brings the longer sides of the slit into parallelism with the level lines of the ground being recorded. The longer sides of the slit 10 are formed by the diametrical edges of two semicircular members 20, 21, adapted to be rotated about their centres O, O<1> by arms 37, 38 respectively connected by links 39, 40, to arms 41, 42 arranged to be rocked by worms 45, 46. The latter are connected respectively to star wheels 31, 32, which may be acted upon by rods which are radially slidable in a wheel 34. The rods are brought out of the wheel 34 as desired and the arrangement is such that the operation of the star wheel 32 lags behind that of the star wheel 31 sufficiently to ensure a uniform exposure notwithstanding rotation of the slot. The ruler 30 is moved to indicate the direction of the slot by links 52, 51, 50, worm wheel 48, and flexible shaft 47 from the star wheel 31. The operator adjusts the distance between the projector frame and the board 8 in accordance with the contours being passed over by the pointer 29 and a counter 54 is provided to indicate this distance. Specification 342,683 is referred to.