Key Technologies For Distributed Virtual Harbour

Using advanced computer technologies to provide navigation information for deck officers or harbor' s traffic managers as detailed and convenient as possible is an inevitable trend of the development of navigation information system. Based on technologies from geographic information system (GIS), Internet, virtual reality (VR) and the demands of navigation application, the thesis proposes a new-style navigation information system, distributed virtual harbor. Based on analyses of its concept and basic characteristics, several key technologies for constructing such a system are researched. In detail, the research contents and contributes of this thesis include the following aspects:(1) proposes the concept of distributed virtual harbor, opening up a new development direction of navigation information system. Distributed virtual harbor is an outcome of combined application of GIS, Internet and VR in navigation information field. It publishes three dimensional geographic data of harbor aria and other navigation related information through Internet, and provides functions of visualization of harbor' s three dimensional geographic environments, navigation information query, spatial analysis, spatial decision, distributed interaction among users, and so on. Distributed virtual harbor can not only provide comprehensive navigation services in a three dimensional platform for users on ship to analysis and comprehend the dynamics sailing environments exactly, but also provide three dimensional interface for traffic managers in land to perform ship' s dynamic monitor and harbor' s traffic management in a convenient way.(2) proposes several technological schemes for constructing distributed virtual harbor, and a feasible system architecture based on the technological schema of VRML plus Java.(3) proposes a technology of Internet based distributed virtual environment, which is used to construct the basic framework of distributed virtual harbor. In detail, a feasible and flexible system architecture is proposed; modeling methods for vary entities in virtual environment are proposed; a compact application communication protocol based on VRML and Java is proposed; a method for dead-reckoning based on reactive behavior model is proposed; a simple collision detection method suitable for distributed virtual environment is proposed.(4) proposes a multi-resolution geometry compression method which can accelerate rendering speed at same time to solve two core problems of distribute virtual harbor that are how to transmit three dimensional models quickly through Internet and how to render these models quickly in client. The method first products a vertices sequence with good locality and continuity by a mesh recursive partitioning based vertices orderingarithmetic and local continuity optimizing arithmetic. The vertices sequence is then used to perform multi-resolution analysis and final geometry compression by a method based on Haar wavelet. The experimental results show that the method archives good compression performance, and supports progressive transmission and multi-resolution represent of mesh, at same time, it greatly accelerates rendering speed of mesh in client because of the rendering sequence related information contained in mesh code. A unify web framework based on VRML for the multi-resolution compression method is further proposed to implement quick transmission and rendering of three dimensional models in distributed virtual harbor.(5) researches the methods by using VRML plus Java to implement GIS functions including spatial information query, spatial analysis and spatial decision support that suitable to the characters of distributed virtual harbor. In detail, for spatial information query, not only the methods for querying static information of natural and sailing environment in harbor, but also the methods for querying real-time and dynamic information of ships are proposed; for spatial analysis, the theory of ship collision avoiding geometry is used to study the spatial relations among ships in distributed virtual harbor, and the graphics represent capability of VRML and Java is used to visualizing results of spatial analysis; for spatial decision support, Fuzzyjess, a shell of fuzzy expert system based on Java, is used to implement a new style ship collision avoiding expert system that satisfies the real-time and network requirements of distributed virtual harbor.(6) based on above key technologies, a proto system of distributed virtual harbor is implemented. The system possesses the basic characters of distributed virtual harbor, and can be used in practice after further improvement.