ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001 
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2 3D MODELING AND EDITING 
In the cybercity, the most important components are the 
buildings and the municipal facilities. So the 3D reconstruction of 
buildings and facilities is a significant work for cybercity. 
According to the LOD (level of detail) concept, CCGIS provides 
three different 3D modeling schemes for different data sources, 
as shown in Fig. 2. The authors agreed with the views of Woo 
Sung Ye (1997), it is better to use the fractal dimensions to 
describe the LODs of 3D city models. The larger the dimension, 
the higher the level of detail, and vice versa. For instance, point 
is 1D and planar line is 2 D, but the DEM surface can be 
considered as 2.5D. The outline box of building is also only 2.5D, 
if the real exterior shape of building such as the roof is 
expressed the model is 2.75D, and the real 3D entity should 
express all the details including the exterior and the interior 
structure. As shown in Fig. 1, there are usually 4 different 3D 
modeling methods for cybercity construction. 
(1) The 2.5D virtual landscape can be generated by 
overlapping the orthoimage onto the DEM surface. 
(2) If designed data such as CAD/3DS/3DMAX is used, the real 
characteristics of geometric structure and texture can be 
expressed. Such kind of 3D city models can reach more 
higher level of detail. Not only the cityscape, but also the 
rooms and the furnishings setup can be expressed 
realistically. 
(3) Based on the photogrammetry, laser scanning and other 
ground surveying means, 3D coded data and real texture 
images can be obtained efficiently to describe the status of 
cityscape. Such kind of modeling methods are therefor used 
broadly for large-scale modelling with multiple scales and 
relatively higher detail level (2.75D). 
(4) Another simple modelling method is to use the bottom 
boundary data of buildings(i.e. the 2D vectors of GIS) and 
its height attributes. Since the city model created by this 
method is only 2.5D (all the roofs are planar), it is usually 
used to express the profile of cityscape with relatively lower 
level of detail. 
Based on the above multiscale modeling methods, from the 
street to each building and even to each room, various details of 
city model can be expressed. Because the CAD based methods 
and the simple method have been used successfully, the third 
method based on the digital photogrammetric workstation (DPW) 
is therefore discussed in detail. Aerial image and close-range 
image are very important data source for building reconstruction, 
especially the DPW provides the most economic and fast 
technique for 3D city data collection. In order to simplify the data 
collection flow, to reduce the workload and to ensure the 
reliability of 3D reconstruction, in CCGIS we recommend the 
following scheme. 
(1) The city model is classified into different basic classes 
(primitive entities) according to the shape characteristics, 
such as point, line, simple entity, multi-entity, sphere, 
cylinder, convex surface, concave surface and upright 
surface, and each voxel is identified by class code and user 
code. Arbitrary complex buildings can be composed by 
these primitives. 
(2) The difficulties of 3D reconstruction (without regard to the 
automatic extraction from image) is mainly the express of 
special roof shape and general concave surface. But based 
on the feature points and feature lines obtained by DPW 
and automatic TIN algorithm, CCGIS solves this problem 
preferably. Fig. 2 illustrates this kind of multi-scale 
modelling. 
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Figure 2 2.5D model generated from the 2D outline 
(b) 2.7D model generated from the 2D roof outline 
Figure 2 Geometric models with different detail levels 
(3) Complex city model then can be assembled in an interactive 
edit environment by using of voxel primitives, and all the 
attributes including texture, material and multimedia 
description also can be related. If necessary the existing 
model can be edited, like to append or to delete any kind of 
object (point, line, surface, or body), to modify the geometric 
shape of buildings such as to change the planar roof to 
herringbone roof. 
(4) All the modeling results are stored in a hybrid system of files