Patent GB-331595-A (GB)
Title: Improvements relating to production of maps by means of aerial photographs
IPC: G01C11/00
Filed: 1929-04-10
Abstract: 331,595. Aldis, A. C. W. April 10, 1929. Photographic surveying. -Stereoscopic aerial photographs, which have been corrected for errors due to the tilt of the camera in accordance with the inventions described in Specifications 329,383 and 330,972, are utilized for the determination of the heights, shapes or contours of the various features in the photographs. Apparatus is utilized which determines a pair of intersecting axes related to reference marks on the photographs and points situated equidistantly along the perpendiculars through the plumb points of the photographs, such plumb points being the points vertically beneath the camera when the photograph was taken. Means are also provided whereby the effect due to the photographs having been taken at different heights is compensated. The geometrical considerations and conditions resulting in the arrangement of apparatus shown diagrammatically in Fig. 16, are indicated in Figs. 12, 13, 14 and 15. The horizontal line A, B meets the curved surface of the ground C, D, in the point Q, of which successive photographs from the two positions S<1>, S<2> of the camera lens are represented by the points n', n<2> on the negatives N<1>, N<2>, the points P', P<2> being the plumb points from the camera positions on the horizontal line A. B. The lines Q S', Q S<2> are shown intersecting imaginary positives T<1>, T<2> at the points t<1>, t2. The essential axes of one form of apparatus are shown diagrammatically in Fig. 13, the photographs T', T<2> being placed so that the line s<1> t' will meet the line s<2> t<2> at the point Q, the ground detail corresponding to the points t', t' appearing as a single point when viewed stereoscopically. Movable reference marks G<1>, G<2> placed on the points t<1>, t<2> will appear as a single mark in contact with the ground at that point. In the construction and operation of the apparatus the photographs T<1>, T<2> are preferably in the same plane, Fig. 14. In this diagram the photographs have been separated horizontally and the vertical distance oetween the points Q<1>, Q<2> corresponds to the difference in level of the photographs T<1>, T<2>, Fig. 13. A horizontal member containing the points q<1>, q<2> can be made to control the axes through s<1>, s<2>, if the ratio of the vertical distance between the points q', q<2> and that between the points Q<1>, Q<2> are the same as that of the distances between the points q<1>, s<1> and Q', S'. The positions of the photographs relatively to the points s<1>, s<2> may be transposed without rotation from positions below the points s', s<2> to positions above them, Fig. 15. The photographs have also been moved horizontally so that the line S<1> G<1> passes through the plumb point of the photograph and a fixed vertical axis passes through the ground detail t<1>. This alteration enables the movable reference marks G<1>, G<2> to be replaced by fixed reference marks K<1>, K<2> on the vertical axes through S', S<2> and the photographs to be movable in a horizontal plane, without rotation, so that the axes S' G<1>, S<2> G<2> pass through the plumb points and can be controlled by a horizontally movable member associated with the points q<1>, q<2>. The arrangement of axes in Fig. 16 corresponds to the upper part of Fig. 15, the rods f, g determine the axis s<1> q<1> p<1> and the rods h, i, the axis s<2> q<2> p<2>. The photographs 40, 44 are carried by the support 38 and the position of the contour mechanism is indicated by the lines through q<1>, q<2>. The apparatus, Fig. 1, comprises four pillars b secured to a base a and connected at the upper ends by side bars c and cross bars d, the latter, together with an addi. tional front bar e carrying the viewing apparatus. The pillars b carry the contour mechanism and the carriers for the photographs. On the pillars b slide sleeves j, two connected together by the bar k and two by the bar l. All the sleeves are moved simultaneously from the handle s through bevel gearing or from the handle wheel v. The positions of the sleeves j are indicated on scales against the sleeves. Rollers x on the sleeves j carry circular bars y forming with cross bars 4 a frame which can slide horizontally. A movable frame is arranged above the bars 4 and comprises end members 5, 6 and longitudinal members 7. This frame can slide horizontally on the bars 4. Associated with the frame 5, 6, 7 are four universal pivots for the rods f, g, h, i, one of the pivots being provided on the member 5 of the frame and the others carried by slides 11, 12, 13, the slide 12 being pinned to the bars 7 and the slides 11, 13 free to slide together on the bars 7 being connected by rods 14, Figs. 6, 7. A table 28 carries the paper on which the contours are plotted by a pantograph 29 connected to the member 5 and the cross bars k. The photographs 42 are carried on a table 38 supported on rods 35 mounted between pivots 34 on sleeves 32 carried by the pillars b. The photographs are mounted so as to be rotatable in their own plane and are illuminated by lamps 90. Since the rods f, g, h, i are pivotally mounted in sleeves 100 and passing through sleeves mounted on the table 5, 6, 7 are connected in pairs to the photograph supports 40, 44 any movement of the photograph will result in a corresponding movement of the table 5, 6, 7 and consequently of the contour tracing pointer of the pantograph 29. The photographs are viewed by the stereoscopic telescope 53. In operation, the height of the pivots on the members 11, 13 above the centres 100, is adjusted to represent the height to some scale at which one of the photographs was taken and the height of the pivots on the member 5, 12 are adjusted in the sleeves 15 to correspond to the height at which the other photograph was taken, by the head 21 and shaft 26. The photographs being centred so that the plumb point is on the axis of rotation of the supporting plate, each photograph is oriented so that with one pair of control rods, e.g., f, g vertical the two plumb points of the photographs and their images all lie in a straight line. The screw 27 is then operated to adjust the separation of the photographs until the reference marks in the stereoscope are seen as a single mark in contact with the ground at the plumb point on the left hand photograph, Fig. 1. The contour at the plumb point level may now be traced. Other contours are traced by adjusting the height of the table 5, 6, 7 by the wheel v.