Review on Three-Dimensional City Model Research
三维城市模型的研究现状评述

The three-dimensional GIS (3DGIS) has been developed for a long time, but with the research work goes further deep, it is found that it's almost impossible to establish a common 3DGIS platform, because objects data modeling and its spatial relationship expression is so difficult. As city is the central place that people living and information spreading, doing research of 3-dimensional urban GIS not only has great significance, but it is also one urgent problem that people want to resolve. Thus three Dimensional City Model (3DCM) research becomes a hot area in GIS field in recent years. The 3DCM research also has great significance in traffic, terra, mine, survey, and other fields, especially in city planning, construction, and environmentology. The 3DCM research has made a great progress in Japan, Germany, Austria, Canada and China. The 3DCM researches have been done abroad, and many works are largely related to specific applications.In addition, people still have no common understanding to 3DCM concept and its research meaning. In this paper, the authors consider that the `3-Dimensional City Model' is a suitable concept, and 3DCM content meaning should include: various 3D entities data modeling, huge data management, 3D spatial relationship expression and operation, 3D spatial data storage, manage and query, and large city area real-time visualization etc. To 3DCM theory research works, methods used in data modeling could be classified into three types: method based on DEM and images, method based on primitives and 2DGIS, and method based on 3D data structure. For data management, the majority of systems are still using 2DGIS, while 3D expression only used in 3D visualization, and few systems manage and express 3D objects using 3D expression in its fundamental. At present 3DCM mainly uses CAD to establish objects model, and 2DGIS has managed a large number of data, so the main research works focus on 3D data and texture capture, as well as 3D objects reconstruction based on images. Although 3DCM research works have got a rapid progress, many problems still exists, e.g., data modeling needs further research works. Present model could only express regular 3D entities, and it's difficult to express complex 3D entities. At the same time, present 3DCM system could only provide animation and fly functions, and many research works still need to be done in side of spatial query and spatial operation.