Patent GB-858479-A (GB)
Abstract: 858,479. Surveying instruments. GAMMA OPTIKAI MUVEK. Sept. 8, 1959 [Sept. 10, 1958], No. 30672/59. Class 97(2) The invention relates to method of surveying in which a tacheometer is sighted on the zero mark of a horizontal staff and then by horizontal rotation of the alidade through a small angle the intercept read off on the staff gives a direct reading of the distance of the place at which the staff is set up from the tacheometer position, reduced to the horizontal, and is concerned with so adjusting the small angle through which the alidade is rotated that it is proportional to the sine of the angle of the alidade as read on the normal horizontal circle of the tacheometer. Another reading is then taken where the small angle through which the alidade is rotated is proportional to the cosine of the horizontal angle of the alidade and the intercepts read off. the horizontal staff give the position where the staff is situated directly in terms of its two rectangular co-ordinates. As shown, the horizontal circle 1, Fig. 6, is graduated as usual in degrees but both outer and inner ends of the graduation lines are numbered. The various optical components 2, 5, 6, 8, 11, 12, 13 and 14 are provided to produce an image at 15 and a semi-circular half lens 3 of long focus and an oblong half lens 4 of the same focal length are positioned as shown, the half lens 3 being rigid with the alidade but the half lens 4 being displaceable horizontally as shown by the arrow, Fig. 7. This displacement is brought about by mounting the half lens 4 on a frame 18, Fig. 9, which can slide on guides 20 fixed to the alidade. An eccentric 17 is movable along grooves 21 of the horizontal circle holder 16 so that its eccentricity is adjustable and then it is secured in the required position so that it is rigid with the holder 16 and horizontal circle 1. Thus on rotation of the alidade, the guides 20, rigid therewith, are rotated, and, through eccentric 17, frame 18 and half lens 4 are displaced a distance proportional to the sine of the horizontal angle of the alidade. A typical image in the reading microscope is shown in Fig. 3, the upper part image being produced through half lens 3 and the lower part image through the displaced half lens 4 so that the separation of the upper and lower graduations 74 is proportional to the sine of the horizontal angle. On tilting a planeparallel glass body 7 by means of a micrometer screw, not shown, the entire image can be displaced from that of Fig. 3, to that of Fig. 4, in which the lower part image has graduation 74 centered on the double line provided on the graticule plate 10. On rotation of the alidade so that the upper part image has graduation 74 centered on the double line, as shown in Fig. 5, the small angle of rotation is proportional to the sine of the angle on the horizontal circle and the intercept on the horizontal staff can be read off. If now the horizontal circle is rotated through 90 degrees and the method repeated, the small angle through which the alidade is rotated is proportional to the sine of 90 degrees plus the horizontal circle reading, i.e. the cosine of the horizontal circle reading. The flat prism 9 ensures that the two part images have each passed through only one of the half lenses 3, 4. In a modification, the half lens 4 is replaced by a pair of glass wedges which are rotated in opposite directions in accordance with the angular movement of the alidade. The horizontal staff may have its zero at one end or have it centrally in which case the graduations to one side of zero are coloured red and those on the other side black.