Research on 3D symbolic representation of geographical information

The symbolic database system is the basic tool of geospatial data representation in map. In the past, many researchers didn´t focus on 3D map symbols but mostly on 2D map symbols. In 3D GIS, all geographic phenomena and spatial entities need to be represented by the corresponding 3D symbol models. So establishing a complete set of 3D map symbolic database with expression becomes critical in technology development of 3D map visualization. Based on the theory of map information transmission, the categorical rule and drafting law are researched and a principle of establishing a 3D symbol is presented in this paper, which contains two aspects The one is that all kinds of spatial feature information which are suitable for description by 3D symbol models have been identified, the other is that it should be implemented at the viewpoint of computer graphics and visualization. And the basic concept of 3D map symbol model and the relation between traditional 2D symbol and 3D map symbol are stated, which include (1) 3D symbol is not to deny or abort using 2D symbols, but to complement and enhance 2D symbols; (2) 3D symbol enriches and augments the way of map representation, promotes the study on the latest 3D area of cartography, and acts as critical role on research and development of new map visual products. Meanwhile, a principle of generating a 3D symbol is also proposed, which are (1) description in abstraction and visualization; (2) logicality; (3) conciseness; (4) feasibility. The research in this paper lays theory fundament for establishment and applications of 3D symbol database. In addition, the approach and basic procedure of 3D symbol modeling is given in detail which consists of 3D entities modeling, symbol render and assignment processing, scenery conflating of 2D symbol and DEM, symbol algorithm design, etc. The technology of texture gradational blending is adopted to deal with the crack of rendering line symbols and area symbols caused by boundary transition, - - which can implement the boundary mutation on the condition of texture rendering of line and area symbols and realize a perfect visual effect. And the boundary model(BR), parameter model and construction entity geometry(CSG) method are integrated to represent the symbol spatial information in design an entity model, which finishes the structure design of symbol figure information. As the basis of 3D geographical language, 3D symbol model has broken through the traditional 1D literal expression and 2D abstract symbolic expression, promoted the emergence of 3D and multi-dimensional language and made the traditional 2D static geographical language develop into the 3D and dynamic scenes representation. Research on 3D symbol model can make great significance for further understanding the essence of three-dimensional GIS, normalizing the 3D model, expanding the area of 3D GIS application, and so on.