Patent GB-1100812-A (GB)
Abstract: 1,100,812. Photogrammetric calculating. BENDIX CORPORATION. 4 Aug., 1966 [30 Aug., 1965], No. 35010/66. Heading G4G. [Also in Division H4] General.-The Specification describes automatic contour or profile plotting photogrammetric apparatus wherein differences in the two stereo photographs caused other than by parallex effects, e.g. pitch variation of the aircraft, atmospheric diffraction, and optical defects-are counteracted by corresponding variation of the motions of the light spots respectively scanning the two photographs. The two photographs are of a surface Z = F(X, Y) and a point 0 (X, Y, Z) on this surface is transferred on one photograph to a point 0<SP>1</SP> having co-ordinates x 1  = F 1 (X, Y, Z), y 1  = F 1 (X, Y, Z) and on the other photograph to a point 0<SP>11</SP> having co-ordinates x 2  = F 2  (X, Y, Z), y 2  = F 2 (X, Y, Z). It is the inclusion in the transfer functions F 1 (X, Y, Z), &c. of factors other than parallel that necessitates the above mentioned scanning variations. Thus when a scan generator 20 produces a scan motion #X, #Y relative to the surface Z, these are changed in scan shaping means 22 for use on the two photographs to #x 1 , #y 1  and #x 2 , #y 2  respectively, according to the formulµ The partial derivatives #x1/#X, &c. are provided by means 24 and the surface slope components #Z/#X, #Z/#X are provided by means 26. First approximations of the surface Z = F(X, Y) or " model " are produced by means 34 for continuous correction by reference to the detected parallex and correlation between the points scanned in the two photographs. If a contour is to be plotted, then the produced value of Z is fixed, and if a profile is to be plotted along a bearing γ, then the ratio of X to Y is kept constant. The produced values of (X, Y, Z) are transferred to the photograph co-ordinates x 1 y 1  and x 2 y 2  respectively, by means 30 according to the given transfer functions. These co-ordinates are used to position the respective photographs 52 and 54, Fig. 3, along respective X and Y axes, so that the scanning spots for both photographs, produced by a respective C.R.T. 40 and 42 under the respective control of the changed scan motions #x 1 , #y 1  and #x 1 , #y 2 , should scan the same points in each photograph, such that analysis of the resultant video signals V 1  and V 2  produce maximum correlation C and zero parallel P. The correlator 32 also produces signals representing errors ESx and ESy in the assume component slopes Sx and Sy of the model and feeds then for integration at 26 to produce the surface slope components The contour or profile co-ordinates X, Y, Z  are after fed to a recorder 35 for reproduction. Scan Shaper, Fig. 2 (22 in Fig. 1).-This analogues equations (1) shown. Correlator, Fig. 4 (32 in Fig. 1).-The correlation function C is produced by multiplying the video signals V 1  and V 2  at 76, and filtering the product. The parallex function P is prodV 1  d#x duced by multiplying V 2  by - and - and dt dt filtering the product. The unfiltered parallex function is multiplied with the scan motions #X and #Y and the products filtered, to respectively produce the slope component errors ESx and ESy respectively. Plotting Motion Generator, Figs.- 6a, 6b, 7 (34 in Fig. 1).-(A) Contour mode, Figs. 6a, 6b. To accentuate the increase of the correlation function C and the decrease of the parallax P when registration of the photographs is  neared functions F(C) and F(P) are derived in respective generators 108, 110 and are multiplied to give a signal determining the contouring velocity V. A parallex correcting velocity W is used at right angles to velocity V, proportional to P and the reciprocal of the surface slope Sm, where Sm = #Sx<SP>2</SP> + Sy<SP>2</SP> + k4  : 1/Sm is therefore produced by squares 100, 102, a summer, and an inverter square rooter 114, and W produced by multiplier 116. If # isthe direction of the surface slope, then the components of the plotting velocity are: and the corresponding X and Y co-ordinates are given by the time integrals thereof The value of Z is kept constant in the contouring mode. The above equations are analogued by circuits 126, 128, 130, 132, 134, 136, 138 and 140. The slope direction # may be expressed by the equations shown in Fig. 6a, whence means 104, 106, 118, 120, 126 are used to analogue these equations, or it may be expressed by the equations shown in Fig. 6b where the means shown in that figure are seen to analogue said equations. (B) Profiling mode. Fig. 7. In this mode, the contouring velocity is produced as before, but so that the co-ordinates X and Y should always lie along the given profile direction #, i.e. the equations are used and analogued by means 180, 168, 172, 170, 174. The parallex correcting velocity W is made proportional to the parallex P, and the height Z of the surface along the profile is made equal to Z = # (W + V.S<SP>11</SP>P.)dt. This last equation is analogued by means 190, 188, 176, 178. The slope signal S<SP>11</SP>p, is given by the equations shown, and these equations are analogued by means 182, 184, 186, 188.