An image ranging system at sea

Abstract

In a current experimental automatic navigation system, the Automatic Radar Plotting Aids ( ARPA ) is a device t o a c q u i r e navigational informations about ships in the radar visibility. We are de\,eloping image processing techniques for calculating the distance to a target ship based on processing s c e n e r y pictures, which has been originall), obtained from \,isual images and used as navigational informations by ship operators. This scheme is realized bj. measuring a minute angle between the horizon and the waterline in a scenery image and computing the distance to a target. In this paper, we describe 1 ) the derivation of theoretical equations for calculating the distance to a target by means of t h e c o m p u t e d m i n u t e angle, 2 ) t h e verification for the efficiency of the Mouse Pointer Ranging Sjstem, and 3) the development of semiautomatic s y s t e m h e l p e d b y image processing techniques, that is named the Semi-automatic Image Kanging Sj.stem.We hai-e tested the accuracy of their calculations by applying 148 pictures a n d 214 images to the ranging sj.stems. It is possible for the both image ranging systems to measure the distances a t the error rate of less than 11 or 1 3 percent of ARPA radar distances. The accuracj. is good enough for practical use in order to apply to ship handling for avoidance. NRODIJCTIONShip o p e r a t o r s w a n t t o o b t a i n manifold na\.igational informations a b o u t s h i p s a r o u n d themselves. Especially, the informations of distances between them and own ship are the foundation informations for safty navigation. Kanging systems for ship avoidance have been developed and tried to apply to automatic na\.igation systems.(l] Recently, a n ARPA radar has been generally employed for a senser to obtain the naligational informations in the automatic na1-igation s!.stems, but fulfilling function o f ship operators' ej.esight is not realized in the ARPA (Miliogaoka, lbaraki, Osaka 567, JAPAN) radar. The ARPA radar is a useful ranging system by using a microwave, however, they have phenomena such as false echos and swapping targets. For these reasons, the ARPA radar cannot occasionally offer necessary navigational informations to ship operators. When the ARPA radar cannot work, ship operators can estimate visually the distance to a target. Therefore, we have paid attention to image processing and understanding techniques in place of ship operators' eyesight, and tried to apllj, them. t o ranging systems at sea. If the systems are realized, we can use them which a r e not based 011 the radar techniques. 'I'he new ranging system is expected t o realize high reliability of full-automatic na\:igation systems.At the first step of this study, the ranging formulas are derived for measuring the distance between a target a n d own ship. The formulas a r e basicall). functions of the minute angle between the horizon and the waterline in a scenery image. The horizon is followed the vanising point. [2] At the second step, for confirming the availability of the ...