Patent GB-280237-A (GB)
Title: Process of and apparatus for plotting photographs of the country for mapping purposes from air photographs
IPC: G01C11/00
Filed: 1927-11-07
Abstract: 280,237. Boer, I. Nov. 6, 1926, [Convention date]. Photographic surveying.-In order to determine the tilt of the camera used in taking an aerial photograph so as to facilitate mapping the country which they cover, a number of reflecting devices such as heliostats or mirrors are arranged around the horizon so as to direct sunlight or artificial light towards an auxiliary camera on the aircraft and there are provided in connection with the said camera a number of reflectors around the optical axis to direct the light from the heliostats &c. on to the plate. The desired angle of tilt is obtained by projecting the images thus produced on to a similar reflector system and thence on to a series of screens as described below. Fig. 2 shows diagrammatically the reflectors and screens. Eight reflectors, of which four (1, 2, 5, 6) are shown, are used arranged in two tiers, and a like number of screens such as S1, S2, S6, S7. The images produced by the reflectors on the plate are denoted by the letters C, D &c. In projecting the images, each of the screens is placed in the focal plane of the image 01 of the objective A in the corresponding mirror and is marked with a series or hyperbolas representing the sections by the said plane of a number of cores having 01 as apex and various vertical angles. The plate is mounted so as to be displaceable in two directions at right-angles to each other. The angle of inclination of the ray producing a given image being known, the plate is adjusted until the projected image falls on the hyperbola appropriate to the said angle, and the desired angle of tilt is obtained from the amount of adjustment imparted to the plate. Instead of using a series of screens as above, a single photograph containing images of all the hyperbolas can be obtained by means of the reflectors and this photograph can be placed against the displaceable plate for direct comparison. Fig. 3 shows a heliostat employed to direct sunlight towards the camera. A telescope 11 can be rotated about horizontal and vertical axes 12, 13 and is kept directed towards the aircraft. A mirror 17 is mounted on the axis 13 at an angle 45‹ to the horizontal and another mirror 14 is mounted so as to be rotatable around vertical and horizontal axes 15, 16, the point of intersection of which lies o:a the axis 13. The mirror 14 is geared to the telescope so as to rotate around the vertical at half the speed of the latter. The inclination of the telescope to the horizontal can be read on a scale 24. With this arrangement a ray 28 incident on the mirror 14 is reflected by both mirrors so as to be transmitted in the direction 30 which is parallel to the axis of the telescope and is therefore directed towards the aircraft. The apparent movement of the sun is followed by means of adjusting-screws 21. 22, 23, reflecting prisms 32, 33 being provided to direct part of the light into the telescope so as to facilitate adjustment. The horizontal motion of the aircraft is followed by turning handles 34 carrying toothed wheels 35 gearing with a rack on the ring 36. Means are provided whereby the reading of the scale 24 at the moment of taking the photograph is made known.