Patent GB-1490397-A (GB)
Title: Parallel line scanning method for stereo-mapping
IPC: G03B35/00
Filed: 1975-01-27
Abstract: 1490397 Photogrammetry BENDIX CORP 27 Jan 1975 [13 Feb 1974] 3415/75 Heading H4D In a photogrammetry system the images are each notionally divided into a matrix of regions 6-10, Fig. 1, arranged in parallel lines 1-5 and scanned perpendicular to said lines whilst the images are mechanically moved in the direction of the lines. After digitization of the resultant video signals, a parallax difference is determined for a scan of one region-e.g. 6-and stored until the region is next scanned whence it is used to pre-shift one video signal relative to the other to lessen the amount of shifting needed to bring about maximum correlation and so quicken the overall scanning of the images. The regions may be completely individually raster scanned in succession, Fig. 1A, whence the movement of the image causes each region to be moved along its line relative to the preceding one, or a single line scan, e.g. 18, Fig. 1B, may scan across all the regions, the resulting video signal being sampled to define the regions. The latter method is preferred, the line scans being along epipolar lines. In the arrangement of Fig. 3, the two images 106a, 106b are scanned along epipolar lines by laser beams 104a, 104b from laser 100, and moved by servos 107a, 107b. The resulting video signals are digitized at 111a, 111b and positionally (time) corrected for geometric, e.g. warpage errors in the images, by geometrical address modifiers 112a, 112b. The digitized video signals for one line scan are fed via preprocessor interface 113 to a preprocessor 114 from whence, segments A<SP>1</SP> and B<SP>1</SP>, corresponding to the video signals produced when corresponding regions in the two images are scanned, are fed to a buffer memory 116. To enable correlation (relative shifting), corresponding segments A and B are extracted from the memory, fed to the parallel processor 117 to generate correlation data. The correlation data is then evaluated and parallex computed at 118. The address for the data segments to be correlated are sequentially generated at 115. Due to parallax, however, the corresponding imagery on the two images is physically displaced, requiring extensive shifting of the data in the corresponding segments to find the initial shifted relationship necessary to produce maximum correlation. The initially generated segment addresses are therefore modified by the parallax data from 118 found during the correlation of the preceding data blocks whereby the segment address for one of the data blocks is shifted so that the selected segment has the same shifted relationship where maximum correlation was found during the correlation of the corresponding segment in the preceding data block. The amount of shifting necessary to find the shifted relationship between the two segments to establish maximum correlation is reduced, as is also the size of the segment required to establish correlation. The speed at which the correlation process can be performed is increased. The parallax signals are also transmitted to the control logic which generates the required mapping signals.