Patent GB-742467-A (GB)
Title: Improvements in and relating to methods and apparatus for stereo photogrammetry
IPC: G01C11/00
Filed: 1952-01-15
Abstract: 742,467. Stereogram metric plotting. ODLE, J. E. Jan. 15, 1953 [Jan. 15, 1952], No. 1149/52. Class 97 (1). A method of stereo-photogrammotric plotting comprises moving two projection systems disposed relatively to a datum plane for plotting in a manner geometrically similar to the dispositions of the taking cameras relative to a datum plane for the terrain to be mapped so that the ends of a -line joining corresponding selected points in each projection system move in a plane or parallel planes and the line remains parallel with itself during the movoments while the plotting table remains stationary, the images being stereoscopically viewed and the systems being moved to bring selected corresponding points of the images successively into stereoscopic coincidence at a position defined by a floating mark associated with the plotting table and effecting actual tracing of the stereoscopic model by remote devices moved in relationship to the movements of the projection systems. As shown, a triangular framework of uprights 1, 2, 3 each having screw levelling feet and connected by cross-bars 8 supports a pair of bars 9, 10 along which a carriage formed by plates 11, 12 connected by bars 13, 14, 15 is movable by a worm 36 which engages a half nut 37 secured to the carriage and is rotatable through a gear-box 41 by a hand wheel 38, and a second carriage formed by plates 18, 19 connected by bars 20, 21, 22 is movable along the bars 13, 14 by a worm 42 which engages a nut fixed to the second carriage and is rotatable by gears slidably keyed to a shaft parallel to the bar 10 driven through a gear-box 45 from a hand wheel 43, both carriages having a roller riding in its first-mentioned guide bar and two V-shaped guides sliding on its second guide bar. Each of two projectors having tip, tilt and swing adjustments about the upper node of its objective is mounted on the second carriage by V-guides engaging the bar 22 and a roller bearing against the bar 21 and is movable therealong by hand to vary their spacing. Each dispositive is held on the projector body 32 by two pairs of clips, one of each pair being a screw-adjusted lever allowing rocking adjustment of the diapositive and the other is sprung to hold the diapositive against the adjustable clip. Beneath the projectors is a housing 48 having a vertically slidable bracket 53 movable by a worm 54 (both on Fig. 2, not shown) rotated by a foot wheel 55, said bracket carrying the viewing stereoscope and a transparent graduated contour height scale 57 illuminated by a lamp 59 (both on Fig. 2) and viewed by a periscope system 64 carried by the housing which also carries a lamp and lens illuminating the floating mark. This housing can tilt about a pivot 49 (Fig. 2, not shown), in a yoke 50 which is itself pivoted at 51 to the main frame work so as to bring the plane of the stereoscope parallel to that of the datum plane of the stereoscopic space image formed with the projected photographs. The stereoscope is provided with a ground glass disc having a small aperture serving as half of the floating mark beneath each of its field apertures and on to which are projected the images of the portion of terrain under examination, each of the discs being continuously rotated to reduce grain by non-self starting electric motors comprising a fixed electromagnet and one or more pieces of soft iron on the disc perimeter. By moving the foot wheel the stereoscope and hence the floating mark are moved vertically to select the desired contour, an auxiliary objective for each projector being adjusted by this movement if necessary to keep the space image in focus, and by rotating the hand wheels 38, 43, each moving the two projectors in unison the floating mark may be brought into apparent contact with the ground at that height on the space image of the terrain and then caused to follow the contour. Simultaneously the rotation of the worms 36, 42 cause movement of a stylus over a remote vertical drawing board mounted on levelling feet, the stylus being mounted for vertical movement by a worm driven through bevel gears one of which is slidably keyed to a shaft driven from the work 42 through a universally mounted shaft 93 along a beam which is itself movable from side to side of the board by a worm driven from the worm 36 through a universally mounted shaft 92. The scale of the plotted terrain may be altered by employing worms of different pitch. To permit the projection of both the images with white light, only small portions of the photographs are illuminated at any one instant so that overlap is avoided, the lamphouses 78 being carried on arms 79 mounted in gimbals centred on the upper node of the projection objectives to move about arcs perpendicular to the light beam for this purpose.