The Design and Implementation of China Continental GIS Platform

To provide a platform for integration of multidisciplinary data from all available transects and derive a 3D lithosphere structural model for China continent,a GGT GIS is to be established. In a broad sense,data incorporated into the GGT GIS,named GeoTransGIS,are in two types,2D data and 3D data,respectively.Therefore GeoTransGIS should contain 2D and 3D functional modules.For the future expandable flexibility and convenient integration of special modeling,a relative independent 2D GIS development scheme based on Titan GIS toolkit is adopted.Meanwhile,3D modules,forming the GeoTransGIS together with the 2D GIS,are developed separately.The 3D modules include 3D-entity model,3D database and 3D visualization functions. Among the problems encountered in the development of 3D GIS,3D data model is the most difficulty one.Presently,there are some 3D data models,namely,wireframe representation,boundary representation (BR),cell-decomposition,construction expression,octree,tin,etc.Although these models are efficient in special application environments,all of them cannot describe the complex 3D entities respectively.Thus,someone created some omnibus 3D data models,which still have shortcomings in the scope of applications.We put forward a 3D GIS object-oriented (OO) data model based on the OO technology and practical application.We treat every entity as one object,and each object has its own state and behavior; two or more objects can form a complex object.In this OODM,there are basic class,entities dividing,3D points,3D line,and 3D surface classes.In order to enhance OODM's descriptive power,we used some existing comparatively mature 3D mdels,such as,octree,function description,TEN,BR,etc.Through the semanteme of OO technology,such as class,object identifier,encapsulation,inheritance,multiple class,etc.,the OODM can not only describe anomalous 3D entities themselves and the complex contact situation among them,but also organize 3D data effectively. Basing on practical application,we realized high performance object-oriented database (OODB) by extending SQL Sever to support 3D spatial data management by adopting object-oriented language (OOL) and open database conectivity (ODBC) technology.Thus,we can manage and manipulate both 3D data and its attribute effectively. All the GeoTransGIS programming work is separately done in VC⁺⁺ 6.0 enbironment.It is through the adopting OO technology that we realized the seamless combination of the 2D and 3D moduls effectively and easily. GeoTransGIS has been applied to the establishment of China GGTs.An example is given to illustrate the feasibility and effectiveness of the GGT oriented GIS platform.