Patent GB-651687-A (GB)
Title: A new or improved stereogrammatic plotter
IPC: G01C11/00
Filed: 1948-11-26
Abstract: 651,687. Stereogrammetric apparatus. KEMP, R. C. Nov. 26, 1948, No. 30719. [Class 97 (i)] A stereogrammetric plotter for use with aerial photographic prints comprises a base-plate for supporting two prints, aT-square movably mounted on the bed-plate, a guide constraining the butt of the T-square to move lengthwise over the plate, three carriages linked for common motion along the blade of the T-square, of which two adjacent carriages have indexing marks moving over the photographs which are viewed through a stereoscope carried by one of the said two carriages, and the third carriage carrying a pencil or other recording stylus, means being provided for automatically varying the distances between the carriages to correct for errors in the photographs. The arrangement is such that as the T-square and associated carriages are moved over the prints, guide rails and wedges automatically vary the distance between the carriages to compensate for lack of correspondence, for tilt and shutter error, and for height displacement in the prints. As shown in plan in Fig. 1, the butt 14 of the T-square slides along rails 17 and the blade 15 has an extension 33 sliding on rails 17 and slidably supports a carriage 20 bearing the plotting pencil 23 pivoted about horizontal axes 26, the right-hand carriage 21 connected to an auxiliary sliding carriage 30 bearing the stereoscope (not shown) and the left-hand carriage 22, the carriages 21, 22 also being connected, as described later, to plates bearing index marks 48, 148. Carriages 20 and 21 are held together by a rod 36, Fig. 3, fixed to carriage 21 and pressed by a spring 38 against a bell-crank 37 pivoted to the carriage 20, and similarly carriages 21, 22, respectively, have pivoted bell-cranks 40, 41 held by a spring 39 against the ends of a rod 42 so that the carriages can slide together along the blade 15 and their relative positions can be varied by rotating the bell-cranks. The free arm 77 of the crank 40 on carriage 21 rests against a flexible surface 76, Figs. 2, 3, on a mounting 67 of which one end 68 rests against a triangular wedge 58 and the other end 66 rests against a wedge 65 moving on the wedge 58. A wedge 81 also contacts the wedge 58 and as it moves rotates an arm 86 against which the arm 90 of bell-crank 37 is pressed. Thus as the wedge 58 is moved along the blade by means of a micrometer 60, the member 67 rotates to cause crank 40 to move and vary the distance between carriages 21, 22 for stereoscopic observation, and the movement of the wedge also causes rotation of crank 37 to move the pencil carriage relative to the carriage 21 to effect the plotting. The flexible surface 76 is supported by a series of jacks 74 so that the shape may be made parabolic as determined by examination of the photographs so that the distance between the carriages is adjusted automatically for lack of correspondence in the prints. Movement of the wedge 58 also adjusts the pencil for lateral height displacement by means of an extension 62 thereof, Fig. 1, pivoted at 112 to a bar 113 also pivoted to a bracket 116 on the butt 14 by a stud 114 adjustable in slots in the members 113 and 116. Angular variations of the bar 113 caused by sliding of the wedge 58 are transmitted by parallelogram linkages 117, 118, 119 to a rotatable table 120 carrying an angularlyadjustable rail 121 engaged by rollers 122 on an arm 123 which, by means of a rack-and-pinion mechanism (not shown) moves a plate 28 parallel to the butt 14. The lower end of the pencil 23 is spring-pressed against this plate and the pencil, and is accordingly rotated about the axes 26 as the plate is moved. The inclination of the rail 121 varies the correction as the T-square slides along the rails 17. Correction for fore-and-aft or lateral tilt or focal plane shutter distortion is applied by moving both the carriages 21, 22 and correction for lack of correspondence is applied by moving the indices 48, 148 relative to the carriages as the T-square moves along the rails 17. These adjustments are effected by means of rails 91 ... 96, Fig. 1, comprising flexible rails attached to plates, e.g. 99, and engaged by rollers, e.g. 104, on sliding members connected to wedges on the blade 15. The rails may be each curved to a pre-arranged extent by a screw, e.g. screw 130, 131 to suit the correction to the position of the butt along the rails 17. Correcting movement of the carriage 21 is effected by connecting one sliding member to the wedge 65, movement of which rotates the surface 76. Carriage 22 is moved by a sliding cam 105, Fig. 2, engaged by an arm 106 pivoted at 107 and engaged by the free arm 108 of the bell-crank 41. The indices 48, 148 are mounted in arms 44, 144, respectively, so as to be slidable relative to the carriages parallel to the butt 14. Each index mounting is spring-pressed against a member engaging two sliding cams and each cam is moved by a member engaging one of the rails 92-96 whereby correction for lack of correspondence is automatically effected. To effect the fore-and-aft adjustment of the pencil carriage 20 the wedge 81 by which it is adjusted is connected to a pick-up 109 engaging over adjustable rail 110 which causes the necessary movement of the bell-crank 37 as the T-square moves along the rails 17.