Study Of Map Projections For Arctic Navigation And Application In ECDIS

As navigation in the Arctic region becomes a reality due to the progressive melting of the Polar Ice Cap,the strategic value of the Arctic is highlighted,and the impact on our national interests in the Arctic is far-reaching as well as the future development.There is a need to develop particular arctic map/chart.The selection of a suitable projection for the preparation of nautical charts,navigation method and the development of navigation equipment has an important influence.In the polar areas the situation is different.Here the meridians are converging towards the poles,which are the center for the concentric latitude circles.Because the large distortions in areas the Mercator chart becomes useless at higher latitudes.The provision of international norms chart compilation above 80 latitude use gnomonic projection.Because of the lack of systematic,in-depth,detailed theoretical and numerical analysis,specific guidance in the polar areas is not easy to prepare for charts and navigation applications.The decision on the choice of the suitable projection for a particular map/chart is a problem that cartographers are facing quite often.A number of factors influence such decision,which are relative to:a.the shape and the location of the area covered;b.the magnitude and distribution of distortions which are inherent to any cartographic projection;c.specific characteristics which are relevant to the intended use of the map/chart.The primary aim of a logical choice is to select a projection in which “the extreme distortions are smaller than would occur in any other projection used to map the same area”.This has been the main criterion for the selection of suitable projection for the Arctic Region in this study.Besides this criterion the purpose and the indented use of the map/chart determine which property/criterion is important.The main contents are as follows:Firstly,This article analyzed the problems about polar projection used in charts,discussing the advantages and disadvantages common projection exists and its application deficiencies in the polar regions of the charts,developing projection evaluation criteria.Secondly,the distortions of Cylindrical,Conic and Azimuthal projections for the Arctic Region are analyzed.Computation and portrayal of the Tissot indicatrix at different locations.Computation and portrayal of isolines showing specific values of angular and area distortion.They provide a generalized view of distortions from place to place.Computation and portrayal of graphs and tables displaying distortions and their values calculated at one degree interval of latitude.Analysing and comparing these three categories of projection basedon the evaluation criteria to select suitable Arctic projection.Then,a single projector under strict requirements can not meet the requirements of the entire polar charts.The Arctic region is divided into two areas of the Arctic and sub-Arctic.Analysing and comparing projections based on the evaluation criteria to select suitable sub-Arctic projection.Longitude and latitude as well as max deviation of great circle line from straight line on the polar chart are systematically analyzed,and to develop great circle sailing route.Finally,it is necessary to analyse the differences in display methods among the electronic chart and radar image in ECDIS.Analysis of the electronic chart and radar image overlay key technologies and processes.Analysis of the error and correction existed in the electronic chart and radar image overlay system.Analysis of distortions on polar projection chart and radar image overlay display,and correct their errors.