Patent GB-748392-A (GB)
Title: Improvements in or relating to methods of and apparatus for combining the representations in photographs having a common zone and combined photographs obtained thereby
IPC: G01C11/00
Filed: 1951-08-07
Abstract: 748,392. Photogrammetry. POIVILLIERS, G. J. Aug. 7,1951 [Aug. 4, 1950], No. 18634/51. Classes 97 (1), 97 (2), 98 (1) and 98 (2). A method of combining the representations in two photographs taken from different viewpoints and having a common zone comprises defining by homologous lines in each of the photographs a single line in the area appearing in the common zone and subjecting one of the photographs to an anamorphosis such that all the points on the homologous line in one of the photographs have corresponding points in corresponding positions on a connection line which is congruent with the homologous line in the other photograph, the anamorphosis consisting of expanding or contracting narrow strips of the photograph extending between an arbitrary line of origin which traverses the photograph from one edge to the opposite edge and the homologous line on the same photograph and/or rotating the strips, while keeping fixed the positions of the ends of the strips at which they meet the line of origin, so that the positions, after anamorphosis, of the ends of the strips remote from the line of origin lie on the connection line, and joining the representations along the connection line in the anamorphosed photograph and the homologous line in the other. If desired, both photographs may be subjected to anamorphosis so that the homologous lines are both converted into congruent connection lines. The photographs 1, 2 in Fig. 1 are overlapping views taken from different viewpoints. Lines of origin O1 O2 extending from edge to edge of the photographs are arbitrarily selected. Lines R1, R2 extending across the photographs are homologous lines, i.e. they represent in each photograph a single line on the ground in the region of overlap, this line being as straight as possible. The photographs are anamorphosed, e.g. by apparatus described below, by rotating and/or contracting or extending successive strips in each photograph. The strips originate from points such as p1, p2 on the lines O1 02 respectively, and terminate at points m1, m2 on lines R1, R2 respectively. Points p1, p2 lie on a line parallel to the line joining the centres w1, w2 of the photographs and passing midway between points m1, m2. In the anamorphosis, the strips p1 m1, p2 m2 are converted into strips p1 m1<SP>1</SP>, p2 m2<SP>1</SP> approximately parallel to w1 w2, the strips being rotated through approximately equal and opposite angles. The points m1<SP>1</SP>, m2<SP>1</SP> lie on congruent lines R1<SP>1</SP>, R2<SP>1</SP> which, when they are superposed lie at all points approximately midway between the lines R1, R2. The anamorphosed photographs may be joined along the lines R1<SP>1</SP>, R2<SP>1</SP> without any discontinuity being apparent. Alternatively, one of the homologous lines R1, R2 may be converted by anamorphosis into a connection line congruent with the other homologous line. A photograph, which has been anamorphosed for joining to another by one of the methods described above, may be joined to the next photograph in a series by further application of the methods. Applications to series of stereoscopic pairs are also described. An anamorphoscope for carrying out the methods described is shown in Fig. 6, wherein photographs 1, 2 to be anamorphosed are mounted for vertical movement, illuminated by a lamp 10, and projected on to translucent screens E1, E2 by lenses L1, L2, the optical axes of which are parallel and perpendicular to the photographs and to the screens. The screens bear reference marks r1<SP>1</SP>, r1<SP>2</SP>, r1<SP>3</SP>, r2<SP>1</SP>, r2<SP>2</SP>, r2<SP>3</SP> lying on a horizontal line, the central mark on each screen being fixed and the outer marks being adjustable. The images between r1<SP>2</SP> r1<SP>3</SP> and r2<SP>1</SP>, r2<SP>2</SP> are viewed stereoscopically by means of a stereoscope 4, and marks r1<SP>3</SP>, r2<SP>1</SP> are so adjusted that they lie on the representations of a single point in the zone of overlap in the photographs. The photographs are then moved through the apparatus together. The lens L1, L2 are mounted on carriages for axial movement to vary the magnification, the images being kept in focus either by keeping the lenses stopped down, or by.means of automatic focusing mechanism. This movement is controlled by a lever 5 for lens. L2. Dove prisms Wl, W2 are also included in the optical paths for rotating the images, and lever 7 controls the prism W2. In the method at present considered, levers 5, 7 are manipulated during movement of the photographs so that, at any instant, a point on the image of photograph 2 coinciding with mark r2<SP>1</SP> represents the same point on the terrain as is represented by the point on the image of photograph 1 which coincides with the mark r1<SP>3</SP>. Levers 5, 7 carry styli s, t which mark a trace on a strip movable in synchronism with the movement of the photographs. After scanning the photographs, the apparatus is set up again. with the screens E1, E2 replaced by photographic plates or films movable in synchronism with the photographs 1, 2, and with a screen having a narrow slit extending along the line on which the marks r1<SP>1</SP>, r1<SP>2</SP>, &c. originally lay. The photographs 1, 2, the photographic plates or films and the trace bearing strip are all moved in synchronism, the styli s, t, being caused to follow their respective traces, so that anamorphosed images of the required parts of photographs 1, 2 are recorded.