model orientation on the plotter, for coupling with the Orthoprojector or storage unit, for orientation 
check and range limitation, as well as for photographic preparatory work. 30—40 %, of the total time 
are needed for the scanning process on the stereo plotter, average model size and speed (mp : 
mx — 1.3 and v = 5 mm/sec in the orthophoto scale) provided. The latter process can be further 
automated after HOBROUGH succeeded about 9 years ago in verifying by an electronic process [2] 
the correlation of identical image details in two photographs, so far restricted to the stereoscopic 
vision of man. In cooperation with Messrs. ITEK, U.S. A., who have already gained experience 
in the design of an automatic stereo viewer, the 'AnEs', a Correiator has been developed for the 
PLANIMAT. 
Fig. 1 PLANIMAT with 
Correlator attachment 
(K = cathode-ray tubes with 
additional photomultiplier, 
P = photomultiplier tube, 
C = Correlator cabinet, 
S = storage unit, St = con- 
trol box) 
  
In an oriented stereo model the different ground reliefs of the individual model points are characte- 
rized by the presence of x-parallaxes. By appropriate raising or lowering of the projection surface 
they are eliminated, i. e. the measuring mark is ‘set’. The problem to be solved thus is to ascertain 
the x-parallaxes electronically, to quantitatively convert them into electric signals and to eliminate 
the parallaxes with the aid of a servo motor, which is inserted in a corresponding circuit as setting 
unit, by ‘zeroing’. The principle design of the ITEx Correlator, details of which are given in a separate 
publication [3], is as follows: 
1) The screen image of a cathode-ray tube is formed on each cf the two stereo images, whereby 
the scanning point covers a closed screen figure by magnetic deflection of the cathode ray. The 
screens are centered and substitute the measuring marks during visual observation. To facilitate 
separation of the signals according to x and y-components, a diamond screen has been selected, 
the scan lines of which are arranged in these very two directions. The shapes of the screens, which 
are to cover identical portions in the two images, change in relation to image-scale variations 
in the corresponding image portions as well as to image and terrain slopes. 
2) With the scanning process, being identical for the two image portions, the scanning rays hit 
image parts of different density. Via the photomultiplier tube these differences in density 
are converted into video signals and, after amplification, transferred to the Correlator. 
3) There, the signals of the two image portions, i. e. voltage shifts as a function of time, are 
compared with one another. The sign of the differential voltage indicates in which direction 
the correction has to be performed. Aslong as x-parallaxes are present, the differential 
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