GB182912A - Method of photogrammetric survey and apparatus therefor - Google Patents

Abstract

182,912. Nistri, U. April 12, 1921. Photographic surveying. - In apparatus and methods, of the kind in which two photographs of the ground to be surveyed are taken from two points at a known distance apart by means of a camera having a lens of known focal length, the orientation and inclination of the camera being also known, and the negatives thus obtained afterwads projected upon a movable screen the positions of which correspond to parallel planes in space, the movable screen, upon which the reference points are first projected to obtain the correct positions of the projecting apparatus, is composed of several parallel sections independently movable in a direction corresponding to the vertical in space. The reference points are first marked on the movable portions of the screen which are then adjusted in position to correspond to the vertical heights of the points in space, and then the negatives ara projected upon the screen from projecting apparatus which is adjusted until the images of the three points coincide with the marked positions on the screens. The negatives together with the two projecting apparatus are then fixed in position and the sectional-screen replaced by a single screen which may be removed to examine contour lines. The apparatus comprises a bench 2 supported on pillars 1 carrying a movable carriage 3 supporting a screen frame 5, in which is inserted the frame 10 carrying ground glass portion 11, relatively adjustable by handscrews 14. The projection apparatus a carrying two or more lamps is carried in a vertical frame 15 and is adjustable vertically and horizontally as shown. The lamps are also independently movable in a transverse direction and are separately rotatable about a vertical axis. As mentioned, when the negatives have been correctly adjusted in position so that the images of the reference points coincide with points drawn on the partitioned screen sections the projecting apparatus is fixed in position and the screen sections are replaced by a single screen. Contour lines may be plotted by moving the screen parallel to itself into the position corresponding to the vertical position of the contour line and then drawing a line through the points of which the two images coincide.