GB1340568A - Automatic stereoplotting apparatus - Google Patents

Abstract

1340568 Photogrammetry ITEK CORP 28 April 1971 [19 May 1970] 11779/71 Heading H4D In automatic photogrammetric apparatus (Fig. 1) of the kind described in Specification 1,317,546, the sudden incidence of the scanning beams on parts of the respective stereophotographs representing terrain rapidly change in height can result in a loss of correlation and the retention in the scanning of the X parallel data pertaining at the time of loss can result in a prolonged loss of correlation. The present Specification therefore proposes that a decrease in strength below a threshold of the X and/or Y correlation signal causes the scanning beam of one C.R.T. to describe, relative to the standard raster scan of the other C.R.T., on oscillatory scan, Fig. 5, either side of the normal path 122 until the strength of the correlation signal increases above the threshold. The condition responsive circuit 50, track and hold integrator 56 and raster search system 53 which detect the decrease in correlation threshold and cause the search scan of Fig. 5, are shown in detail in Figs. 3, 3a. The X correlation signal at 45 and the Y correlation signal at 46 are both tested for level. The decrease of the X correlation signal alone causes a signal on line 54 after a delay # 1 set by 103 whilst AND gate 106 causes the more serious decrease of both the X and Y correlation signals to give a signal on line 54 after a shorter delay # 2 set by 107. The signal on line 54 gates the square wave output of oscillator 112 through 111 to an integrator 115 which generates the triangular search scanning waveform, Fig. 4 (not shown).