3D GIS Spatial Modeling for City Surface and Subsurface Integration

Abstract

With the rapid development of urban, city space extended from surface to subsurface. As the important data source for the representation of city spatial information, 3D city spatial data have the characteristics of multi-object, heterogeneity and multi-structure. It could be classified referring to the geo-surface into three kinds: above-surface data, surface data and subsurface data. The current research on 3D city spatial information system is divided naturally into two different branch, 3D City GIS (3D CGIS) and 3D Geological Modeling (3DGM). The former emphasizes on the 3D visualization of buildings and the terrain of city, while the latter emphasizes on the visualization of geological bodies and structures. Although, it is extremely important for city planning and construction to integrate all the city spatial information including above-surface, surface and subsurface objects to conduct integral analysis and spatial manipulation. 3D Spatial Modeling is the key to 3D GIS, and is the basis of 3D GIS. All kinds of 3D spatial modeling methods are different with the difference of modeling objects. Based on the difference of spatial modeling objects, 3D spatial modeling methods are divided into two kinds, one is Geographical Spatial Modeling, and another is Geological Spatial Modeling. With the contrast of all the 3D spatial modeling methods, this paper also present some key issues on 3D spatial data modeling for geographical objects, surface buildings and geological objects integrated seamlessly with TIN being its coupling interface. Based on this, the paper introduced the conceptual model of Object Oriented 3D Integrated Spatial Data Model (OO3D-ISDM), which is comprised of 4 spatial elements, i.e. point, line, face and body, and 4 geometric primitives, i.e. vertex, segment, triangle and generalized tri-prism (GTP). The spatial model represents the geometry of surface buildings and geographical objects with triangles, and geological objects with GTP. Any of the represented objects, no mater surface buildings, terrain or subsurface objects, could be described with the basic geometry element, i.e. triangle. So the 3D spatial objects, surface buildings, terrain and geological objects can be integrated together with the TIN being its coupling interface. Based on OO3D-ISDM, an application case in the central business district (CBD) of municipal Beijing are introduced. The case shows that the potential applications of OO3D-ISDM in the domains of digital city, digital geotechnical engineering, and so on.