GB765797A - - Google Patents

Abstract

765,797. Stereo-photogrammetric apparatus. ZEISS - AEROTOPOGRAPH GES. May 31, 1954 [June 13, 1953], No. 16019/54. Class 97(1) Approximately vertical axis aerial photographs are set up on a stereophotogrammetric plotter as if they were truly vertical views and it is stated that a pair of photographs of a plane surface produce, when stereoscopically viewed, a curved surface represented approximately by the equation Z = ax + by + cxy + d (where a, b, c, d, are constants) so that contours can only be correctly drawn if the height correction ΠZ is added to the height corresponding to the actual'distance apart of two stereoscopically fusable marks 60, 61 for each point in the photograph. According to the invention the values x, y, each corresponding to a point on the photographs, are automatically set on computer as the marks 60, 61 are moved over them and the computer indicates the value of Z and/or adjusts one mark 61 with respect to the other 60 through distances equal to the correction which Z undergoes on varying x and y. Preferably, the constants a, b, c and d are set on the computer by means of guides 14, 15 and, as shown in Fig. 1, slide 1 and carriage 30, carried thereon, move in mutually perpendicular directions so that pointers 3 and 31 automatically record the x and y co-ordinates of any point in the photograph. The indination of the beam 26 is uniquely determined by the position of slide 1 on rail Z and the value indicated by the pointer 34 is determined by the sliding contact between member 33 and beam 26. Mark 61 is moved relatively to mark 60 through bell crank lever 72 and micrometer screw 62 is used for the initial adjustment of the spacing of the marks. If the constants a, b, c, d are chosen so that one guide 14 or 15 is parallel to the direction of motion of slide 1, the beam 26 may be pivoted to the slide 1 at one end 24 or 25 respectively. If the correct spacing for the marks 60, 61 is known for four points in the photograph mark 60 may be adjusted to each of the four points in turn and one end of each guide 14, 15 moved at each point until the stereoscopically fused marks touch the ground at all four points. The apparatus is then set up for plotting contour lines by means of a pen attached to mark 60. Another form of the apparatus (Fig. 5) is adapted for a cylindrical surface derived from the previous equation by putting y = x. The axis of the cylinder is parallel to the axis of y and the Z correction for any point on a genatrix is the same for all points on the genatrix, so that it is not necessary for the spacing of the marks to be variable with respect to the y direction. As shown in Fig. 5, carriage 30 is displaceable in the x direction only and, a displacement of x moves slide 1 (carrying beam 26) through a distande x/2 in the same direction.