| Geographic Information System (GIS) appeared in the 1960s, after 50 years of development and progress, with the development of 3D virtual reality geographical information technology becoming mature. It has produced important and profound influence to human life.Facing vast amounts of city level 3D model data, there are mainly two ways for virtual auto-modeling. One is based on image; the other is based on the geometric model. The latter is commonly used in large-scale scene rendering. The way of expressing virtual landscape by using complex polygonal 3D model is often modeling in advance by using 3Ds MAX, Maya, etc. Long modeling period and huge manpower consumption limits the smooth development of 3D virtual reality system.This paper puts forward a kind of automatic modeling method based on vector data. Buildings, roads, green belts and other elements can be quickly built on a large scale on the basis of vector data’s position and attribute information. To a certain extent, it provides a new way of thinking to avoid the manual operation for huge amounts of 3D modeling.In addition, with the emergence and development of the Internet, it is possible for us to share information and spread rapidly in the global scope, which greatly enhanced the timeliness of information and improved its reliability.In nowadays, under the background of the network era, the traditional stand-alone virtual reality platform is unable to meet the requirements of users for the information sharing of the data due to its inherent independence and closure.This paper established an image tiles server for terrain rendering on the virtual reality system based on Web Map Tile Service (WMTS) and detailed the complete service release process. For the contradiction between Network bandwidth and mass spatial data, this paper presents a number of methods on optimization of the data loading, scheduling and efficiency rendering. This paper finally achieved three-dimensional terrain rendering based on the WMTS service standards, the main innovation points and the research results as follows:1) networked 3D virtual reality systemIn this paper, aiming at the improvement of 3D terrain rendering, the author changed the previous stand-alone version to the direction of the network on the basis of the original VRGIS platform; it breaks the local-browsing bondage. To avoid mass data copying and frequently moving, simplify 3D data management and improve the flexibility of 3D virtual reality system, this paper changed the way of request space data from reading and writing the local file to the HTTP request.2) standardized and generalized terrain dataOn the basis of the WMTS service standards proposed by Open Geospatial Consortium (OGC), the author published and shared the 3D terrain data in accordance with the unified global standards and processes, which broke the pattern of "one platform, one set of data" on the traditional three-dimensional system, making it possible that many people share the same copy of the data. In addition, it is easier and more convenient for user to update or replace the base data with the adoption of common data release rules.3) 3D rendering performance optimizationFor huge amounts of data transmission scheduling under the network environment, this paper has put forward some principles of performance optimization, formulated some data access strategy, improved the structure of the code and optimized the program logic. Through controlling the resolution of 3D terrain texture, multi-thread loading and some local cache strategy, the data scheduling and the speed of 3D rendering has greatly improved.Based on automatic modeling technique and the improvement and optimization for networked terrain rendering, the sea-land integrated three-dimensional geographic information sharing service system has been improved. It laid a good foundation to form the real networked and integrated spatial data management and resources sharing service platform. |
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