Research On The Key Technologies Of Three-dimensional ECDIS Terrain Display

Three-dimensional ECDIS is a complicated system which integrates multi-discipline technologies.Some related technologies are applied comprehensively,for example,ocean mapping,database management,computer graphics,3D visualization,virtual reality;,and so on.Three-dimensional ECDIS not only inherits all the functions of two-dimensional ECDIS,but also describes and implements every function from the view of three-dimension,which presents an intuitive feeling for the users and has much more rich display contents.In this paper,the multi-resolution display of three-dimensional submarine terrain is mainly studied to achieve the research of the three-dimensional ECDIS system,The present situation and development overview of 3D visualization at home and abroad are analyzed in this paper firstly.Then the knowledge and technologies relevant with digital terrain analysis etc and their applications in three-dimensional visualization are researched.Meanwhile OpenGI,visualization technology and UML modeling technology are also discussed.Based on the deep study of three-dimensional spatial data acquisition technologies and three-dimensional spatial data models,the main factors needing thinking about in three-dimensional ECDIS spatial data model are putted forward. And level of detail,digital elevation model and quadtree structure are researched, and the basic idea of quadtree constructing terrain,the organization form of spatial data and the labeling method of quadtree nodes are presented.The real-time multi-resolution display technology of three-dimensional submarine terrain is emphasized in this paper.The culling algorithms of nodes out of view and back face nodes are researched,and visibility culling methods based on quadtree structure are presented.An evaluation system of quadtree node error in three-dimension terrain display is built and the evaluation formula is presented. An elimination method is given to eliminate the "crack" phenomenon between quadtree nodes.The data structures of electronic chart three-dimensional terrain display system will be designed by applying UML and OpenGL technologies.The methods of improving the system graphic quality are researched based on the multi-texture and shadow patterns.And the specific acquisition process of the optimal nodes set is analyzed.At last,the terrain display window is created dynamically by using multithread technology,and the functions of terrain roaming,switehing of line and face patterns,words output etc.are implemented.Finally,frame rate chart,which is used to describe the terrain rendering rate,is also presented for the evaluation of the results of the key technologies research and the effectiveness of realization methods of three-dimensional terrain multi-resolution display system.