Research on Three-dimensional Water Resources Information System Based on ArcGIS3. 3D Scene Construction 3.1 3D GIS Software Comparison By reason of three-dimensional display and analysis being a hot direction in GIS, almost all the existing GIS software add three-dimensional modules, and some of them have certain functionality of query and analysis. In the following section, several popular 3D GIS software in China and abroad is compared. ESRI ArcGIS 3D Analyst is the three-dimensional visualization and analysis extension of Desktop software. It adds two specialized 3D viewing applications, ArcScene and ArcGlobe, which extend the capabilities of ArcGIS Desktop and adds additional capabilities to ArcCatalog and ArcMap. ERDAS IMAGINE has a three-dimensional visualization tool named IMAGINE VirtualGIS. It uses OpenGL as its basic graphics language and allows the use of hardware accelerators for geometry or texture rendering. Also the IMAGINE VirtualGIS can be run on both UNIX workstations and PCs. One of the notable advantages of IMAGINE VirtualGIS is the water layer plugin, which allows to flood the entire terrain to a specified elevation or flood individual areas of the terrain. VRMap(Beijing Lingtu Inc) is an open and large-scale component-based 3D GIS platform. The secondary development platform is a 3D engine developed with the aid of DirectX and OpenGL. VRMap is equipped with basic 3D spatial analyzing abilities, such as quantitative analysis, inquiry statistical analysis, topographic analysis, two-point perspective computation, profile observation, flood analysis and sunshine analysis. IMAGIS, a 3D Visualization GIS developed by Supresoft Inc, is a geographical information system based on Digital Orthophoto Map (DOM), Digital Elevation Model (DEM), Digital Line Graphics (DLG) and Digital Raster Graphics (DRG). By combining the techniques of 3D visualized reality with virtual reality, the system can manage the objects in a 3D virtual environment, which realizes WYSIWYG in a sense :“What you see is what you get”. CyberCity GIS(CCGIS) software is developed for digital city construction by Wuhan Geo Inc. Based on the city 3D coding data, GIS data and CAD data collected by the digital photogrammetric workstation, automatically established 3D city models, it has functionality of wide range large-scale city database integration management (DEM+DOM+DLG) and seamless 3D real-time roaming. Unique functionality possessed by GIS as spatial multimedia information 3D display query, model application, analysis and decision-making are contained and expanded. CCGIS can be widely used in the application field such as city planning, city management, information distribution and navigation. 3.2 Technical Scheme —— ArcGlobe This research has requirements in some aspects, including real-time roaming speed, data scale, visual effect and system running stability. By analyzing and comparing capability and usage of several existing 3D GIS software, ArcGlobe is selected as the environment to construct 3D scenes. Any type of data with spatial reference on the 3D surface can seamlessly interact with ArcGlobe, and all the data that are loaded into ArcGlobe can be overlaid and visualized in global extent. ArcGlobe breaks through the size limit of data storage and can display large amounts of data quickly and effectively. That is to say, whether its extent is local or worldwide and whether its size is large or small, the raster, vector and terrain dataset can be processed more intelligently in 3D perspective environment than in 2D. So it is effortless to zoom from a view of the whole earth to a local site with a higher degree of resolution, as well as move, query and analyze data of varying extent. 4. Secondary Development 4.1 System Development Based on COM COMGIS is a kind of methodology of software development which merges the Object-Oriented technology and component technology into GIS. The principle of COMGIS is dividing the main functionality modules into some controls which can be available for different functionality. The final GIS application can be implemented by visualized development tools via integrating various controls regardless of GIS and non-GIS [4]. The GIS development based on COM is essentially a kind of compositive secondary development method. It can not only take advantage of efficient programming capability of visualized development tools, but also exert the comprehensive spatial data processing ability of GIS tools. The method facilitates the water resources information system to be more efficient, stainable, maintainable and easy-to-use. The components technology can facilitate the efficient seamless integration of GIS and hydrologic models [5]. Fig.1 shows the framework of seamless integration of COMGIS and applications.  Fig.1 Framework of seamless integration of COMGIS and applications. |