LINE SCANNERS

Line scanners which employ a rotating reflective polygon 32 to sweep an image of a viewed scene 31 across one or more detector 33 suffer from image distortion towards the edges of the field of view. This problem may be mitigated by arranging firstly that the signal output by the detector be sampled, instant by instant, each sample representing a digitized dot-like portion of the viewed scene, and secondly that the sampling be at such a rate as exactly counteracts the linear distortion, so that as the linear distance on the ground increases - as the angular spacing of the instantly viewed area from some central datum line increases - so the sampling rate increases in correspondence (and thus the number of dot-like portions increases to match the greater extent of the scene). In addition the output of the line scanner may be stabilised against lateral angular movement (roll) of the scanner by sampling each line for a time that is shorter than the time needed to scan the maximum field of view ...

LINE SCANNERS

Navigation apparatus

Navigation apparatus in accordance with the invention uses a Large Reference/Small Scene approach in which a plurality of small scene areas are obtained by viewing the surroundings of a moving object and are compared together with a large reference area to produce a match between them, and hence give an indication of the position of the object with respect to the reference area. The apparatus utilises the fact that the small scene areas are in a known distribution, and correlation maxima should be found having that distribution, other maxima being effectively randomly distributed.

Navigation apparatus

Navigation apparatus

Scene matching navigation apparatus e.g. for aircraft

The apparatus for a moving body has a large reference area and a correlation device (12) which compares a number of small area scenes obtained by viewing the surroundings of the body as it moves. The scenes are correlated with the reference area to produce a correlation surface domain. The correlation surface comprises a distribution of correlation maxima for each scene. A device is provided for finding the overall position of best match between the number of small area scenes taken together and the large reference area.