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# Full text

Title
The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics
Author
Chen, Jun

ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001_
ISPRS, Vol.34, Pai
46
developed which includes 3D visualization and operation about
querying 3D objects and some network analysis. A test area
about 4 km 2 is used to create 3D-city model through CWeb3D
system.
2.1 3D CITY BUILDING MODEL
3D CIYT MODEL ON INTERNET
In order to visualization the 3D city data on Internet, building
the 3D city model on Internet is required. The city model
includes building model and terrain model. Most
required applications of 3D city model are related to
buildings. With the development of modern city, there
are much change in function and shape for buildings of
city area, from small to large, from simple to complex in
shape and structure. However, the terrain of city is simple.
The GRID model is used to construct the terrain model.
Most required visualization applications of 3D city
model are related to buildings. Now the city buildings
become more and more larger and complex. In order to
describe geometrical structure and attribute of large
buildings, layer combined model is used to construct
building model. In this data model, the large building is
divided into some parts and each part is also divided
into some building layers. A building layer is defined by
having the same function, structure or attribute, which
is a concept layer including one or more practical layer.
The roof is considered as an independent layer because
of its particularity. The LC Model is illustrated as follow.
Shape
r Layer 1
Attribute feature
s' Part one (Shapel) 'S
Layer2
Layer3
Attribute feature
Building Part two (Shape2)
v:
Attribute feature
Fig. 1: Layer Combined Model
In LC Model, the buildings can be decomposed into
many basic primitives and roofs. For the reason that
almost all the walls of buildings are vertical, these
primitives can be constructed by a closed polygon with
the assumption that every edge of polygon defines a
wall, the geometry data of the primitives can be stored
by the point group (Xi,yi, x 2 ,y 2 ,..., x n ,y n , Zi,z 2 ) in
clockwise or counterclockwise direction, where Zi is the
height of bottom surface and z 2 is the height of top
surface. At the same time, a sole symbol was assigned
to the every wall surface to mark it. Because of the
complexity and peculiar shape of roof, the roof can be
depicted with lots of triangles, which were created by
outline points and inner feature points.
structure, containing identifiable layer (sub-object).
Every layer has the property of geometry and attribute
like wall, roof, color, material, texture and so on, the
topology among layers is also well described.
Furthermore, it can be linked with different attribute
data or texture data to enhance the reality of buildings.
Compared to other data model, LC model has several
• Not only outer shape of buildings but also
inner object of buildings can be depicted.
• Multiple data source can be integrated in LC
model such as image data, vector data, attribute
data, and so on.
In this model, the buildings are comprised by complex
2.2 CITY TERRAIh
The city terrain is r
building model, th<
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