The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
centimeters. So compared with the traditional photogrammetry 
methods, it has superiority. 
3) all-weather: except digital aerial photography, airborne 
LIDAR belongs to active remote sensing. 
4) rich information: it may obtain not only three-dimension 
coordinates of the ground points, but also simultaneously three- 
dimension coordinates of the objects, such as trees, buildings 
and so on. And if LIDAR is loaded with the CCD, image 
information can be acquired. 
At present, the research and application of LIDAR technology 
has been carried out gradually in our country. For example: 
Professor Li Shukai et al.of the Chinese Academy of Science 
has developed successfully the airborne three-dimension image 
forming system,and Professor Li Qingquan et al.of Wuhan 
University has developed the ground laser scaning surveying 
system, and Researcher You Hongjian et al.of Chinese 
Academy of Science has done research on buildings and 
topography extraction based on LIDAR data, and Dr.Zhang 
Xiaohong et al. of Wuhan University has done research on the 
LIDAR data filtering and objects extraction algorithm.These 
researches have achieved much in the theory aspect. Now, the 
more mature LIDAR commercial system includes ATLM and 
SHOALS (Optech company in Canadian), ALSSO(Leica 
company in America), TopoEye(TopoEyeAB company in 
Sweden), LiteMapper (IGI company in German), Falconll 
(TopoSys company in French), etc. and the more mature 
commercial softwares of LIDAR data processing include 
TerraModeler,TerraScan and TerraPhoto(Terrasolid company in 
Finland). 
In 2006, Shanghai Institute of Surveying and Mapping acquired 
the airborne LIDAR data of 20 square kilometers in the central 
area of Shanghai using ALTM3100 airborne LIDAR system of 
the Optech company. This paper introduces the data processing 
procedure of the airborne LIDAR data and proposes a new 
method to reconstruct three-dimensional city model suitable for 
Shanghai with the help of relevant mature commercial software. 
It also explores a convenient, quick, highly efficient method of 
acquiring three-dimensional data and data processing, which 
solves an important bottleneck in three-dimensional GIS 
development, and which is of a crucial significance to the 
informationization construction of city. 
2. THREE-DIMENSIONAL CITY MODEL 
Three-dimensional city model, the foundation of establishing 
the three-dimensional GIS of city, decides the modes of 
organization, memory and management of the three- 
dimensional data, which directly influences the efficiency of 
browsing, distribution and inquiry analysis of three-dimensional 
GIS data. The three-dimensional city model is of application 
value and can be widely used, such as in the analysis of city 
noise ^ thermal radiation diffusion communication electronic 
wave coverage ^ city security and virtual reality of city and so 
on. This paper adopts object-oriented method, taking 
characteristics of Shanghai and application demand into account, 
and then, presents a new kind of the three-dimensional city 
model. According to the object-oriented thought, all kinds of 
things in the real world may be abstracted into one kind of 
objects with the public attributes, as for the city, the real world 
may be summarized for topography and object based on the 
terrain, so three-dimensional city model includes topography 
model and object model. 
2.1 Topography model 
Topography model usually expresses DHM(Digital Height 
Model) with digital elevation model, whose spatial distribution 
is described by the horizontal system of coordinate x, y, also 
may be described by the latitude and longitude ,whose altitude 
distribution is described by elevation Z. in practice, DEM can 
be expressed by two main methods : Regular grid model(Grid) 
and irregular triangular net model(TIN).they have their own 
merits and defects respectively, Grid model is simple and TIN 
may express undulation topography well. Considering 
topography is flat in Shanghai, the paper uses Grid to establish 
the topography model. 
2.2 Object model 
According to the characteristics of spatial distribution, object 
model in the city may be summarized into: artificial building 
model, horizontal element model, non-horizontal plane-shaped 
element model. 
1) Artificial building model: in a city there are many artificial 
buildings including houses, viaducts and flyovers, bridges and 
so on, so the object models are in greatest need. We use 3DMax 
model tool to build up three-dimensional model for the artificial 
buildings, and realize the data exchange through 3ds document 
format .and 3ds divides the model into spatial triangular nets. 
2) Horizontal element model: the horizontal element refers to 
the one with same elevation, such as lakes, reservoirs and so 
on .its characteristics are there being explicit conditions of 
boundary and there not being change in the elevation value in 
the area. The model is identical with the two-dimensional GIS 
with the only difference that it is three-dimensional coordinate 
point. 
3) Non-horizontal element model: this kind of element mainly 
includes vegetation, green belt and the road. They generally 
covers the undulation ground, and the model may also be 
realized through the triangulation of the boundary polygon. 
Figure 1. Point cloud of Lu Jiazui area of Shanghai