GB876740A - - Google Patents

Abstract

876,740. Photogrammetry. NATIONAL RESEARCH COUNCIL. Aug. 12, 1958 [Aug. 28, 1957], No. 25875/58. Class 97(1) A stereoscopic device 20 is used to view overlapping aerial photographs 16, 17 on carriers 14, 15 mounted for rotary adjustment on carriers 12, 13 movable by motors 23, 24, 25, 26 in perpendicular co-ordinate directions with respect to a carriage 11 movable in perpendicular co-ordinate directions by handwheels 21, 22 relatively to a base 10. The handwheels are operated to bring fresh parts of the photographs into position for observation. The motors 23-26 are energized from an electronic computer which has a control by which the carriers 12, 13 may be moved to produce relative movement of the photographs to remove parallax between the observed stereoscopic image of a feature in the photographs and a measuring mark in the stereopscope. The setting of this control is thus a measure of the height co-ordinate of the feature. The computer also has settings which take into account of differences between the two photographs, as to conditions of exposure, especially height of exposure and tilt of camera axis, and defects in the individual photographs due, for example, to lens distortion, atmospheric refraction, film shrinkage and curvature of the earth. All these corrections depend on the positions in the photographs of the points under observation and, to enable them to be calculated co-ordinate data are fed to the computer from potentiometers on the shafts of the handwheels 21, 22. The amounts of the corrections fed to the carriers 12 and 13 by the motors 23-26 are indicated by dials 27, 28, 29, 30. The rotational adjustments of the carriers 14 and 15 are effected by graduated handwheels 31, 32. The procedure for initial setting of these adjustments and of the various computer adjustments is described in detail in the Specification together with the detailed schematic arrangement of the computer and the mathematical analysis on which it is based. The computer described is of the analogue type, but a digital computer may be used. As a result of the corrections supplied from the computer, the handwheels 21, 22 rotate in terms of corrected co-ordinate data and their rotations are transmitted mechanically to a plotting table. The photographs may be scanned electronically instead of being viewed by eye. Specification 764,449 is referred to.