An image ranging system at sea

In a current experimental automatic navigation system, the Automatic Radar Plotting Aids (ARPA) is a device to acquire navigational information about ships in radar visibility. The authors are developing image processing techniques for calculating the distance to a target ship based on processing scenery pictures, which have been originally obtained from visual images and used as navigational information by ship operators. This scheme is realized by measuring a minute angle between the horizon and the waterline in a scenery image and computing the distance to a target. In the paper, the authors describe: 1) the derivation of theoretical equations for calculating the distance to a target by means of the computed minute angle, 2) the verification for the efficiency of the Mouse Pointer Ranging System, and 3) the development of a semi-automatic system helped by image processing techniques, that is named the Semi-automatic Image Ranging System. The authors have tested the accuracy of their calculations by applying 148 pictures and 214 images to the ranging systems. It is possible for both image ranging systems to measure distances at an error rate of less than 11 or 13 percent of ARPA radar distances. The accuracy is good enough for practical use in order to apply to ship handling for avoidance