Theory And Key Technology Research On 3D GIS Web Service

Three-dimensional (3D) geographic information web service is not only greatly required by geographic information web service extension and application, but also bringing new solution schemes for 3D geographic information share, mutual operation and integration. Therefore, it has great practical values to be studied. According to problems existed in current research status, theories related to 3D geographic information web service were proposed from the point of abstract cognition model understanding, and some key technique problems were extracted and systematically studied. Finally, research contents of this paper were experimented and tested.Main contents of this paper are generalized as follows.From the inevitable development trend of geographic information web service, research meanings of geographic information web service were pointed out. And then, status, current theories and technique fruits of web 2D GIS, geographic information web service and 3D geographic information web service were analyzed. Finally, main contents of this paper were summed up.Through analyzing and summing up of geographic spatial cognition process, it was found that 3D geographic information service was essentially a geographic spatial cognition historical process. Then, the geographic spatial cognition process was classified by cognition operation and cognition expression. Based on three layer GIS abstract model, an abstract cognition model for 3D geographic information web service was proposed. Moreover, two features of the cognition model were systematically analyzed, while one is web service cognition feature and another one is 3D geographic information feature. Finally, three key techniques of 3D geographic information web service were extracted.Beginning at the classification of geographic information model, and based on region and object method, expression and organization methods of terrain data and object model data appropriate for 3D geographic information service were studied. According to terrain data, the mapsheet based regular grid partition methods and quad-tree organization methods were applied, while according to object model data, CityGML idea based and object-oriented multi-layer modeling methods were applied and managed by the improved R tree index. The improvement of R tree included the combination of quad-tree and LOD layer designing of object model.Possible user requirements of 3D geographic information service were analyzed, and the granularity of different service layer was determined. Based on granularity analysis, seven types of 3D geographic information service, including WTF based terrain data service, geometric fusing based terrain data service, WMS based grid image service, image pre-generation based grid image service, WCF general contract based object model data service, W3DS based 3D scene service and WVS based 3D visual scene service, were designed and implemented through WCF service packaging technique.A user role transition concept was proposed, and the user connection and role transition in web service was classified into two modes, while one is sequential mode and another one is parallel mode. By user role parallel transition, a freshly new method was proposed to solve problems of massive 3D geographic information distribution. Then, based on user role parallel transition, the concept of User Equal Web and connection mode between user nodes was designed, and then massive 3D geographic information distribution was implemented by quad-tree resource positioning.Under web service environments, two structure modes and 2D geographic information service structure were analyzed. Related techniques were utilized to explore characteristics of the geographic information web service. Then, combing the WCF communication technique, client & service application logic for each service was analyzed. And supported by WCF technique, a 3D geographic information web service structure, including service layer, middle layer and user layer, was designed.An experimental system for 3D geographic information web service is designed. Meanwhile a series of methods were designed to improve effects and performance of the system, and finally the methods were verified by practical experiments.