1SPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
and relational database, and an effective R-tree spatial
index is created automatically.
3 INTEGRATED DATABASES MANAGEMENT OF DEM PLUS
DOQ PLUS DLG
From 2D GIS to cybercity, the data management is a critical
problem. In cybercity, because the reconstructed 3D geometry
and rendering, the description of surface character ad material
parameters are the contents of database. If a system is designed
to handle the fully fledged 3D data base of an entire city,
including geometry, photo texture and additional information we
have to be aware of an amount of some hundred Gigabytes of
data. And we know, that visualization must handle perspective
projection and oblique viewing points. Based on the successful
2D database technology of GeoStar, CCGIS improves the 3D
data handling including spatial index, data selection and clipping
in perspective space, data subsection process and dynamic
loading. The hybrid management system of files and relational
database is the first choice, but the object relational database
like Oracle8.i is also supported for some special applications.
Compared with the traditional 2D GIS, cybercity puts forward
more higher requirements for data organization and
management such as,
(1) the integration of data with different types, raster data like
DEM and DOQ, and vector data like DLG.
(2) the integrated applications of multiscale models.
(3) the fast transformation from database to 3D virtual display.
In order for the purpose of fast visualization of 3D cybercity data,
we design an effective data structure combined the R-tree
concept and LOD concept, and use the object oriented method
to organize these data. For example, in CCGIS the geometric
surface has the following structure,
{
object ID, feature ID, surface type(convex or concave, the
concave is consisted with TIN ),3D box range, boundary points
number and 3D coordinates, texture type and mapping
parameters.
}
Surface object is the basic unit of body, the above structure
benefits the general rendering methods based on OpenGL or
DirectX. In order to provide more efficient data access or browse
for a large area or and LOD control, the 3D model data is
organized according to the classified spatial index based on an
extended quadtree code stored as cluster related to the feature
size.
4 3D VISUALIZATION AND INTERACTIVE PLATFORM
Visualization is very essential for interactive operation, which
provides the windows and the tools for designing our habitation.
Under the support of virtual reality technology, with the help of
the visualization, the cyberspace replaces the traditional abstract
2D map and the descriptive documentation used to explain,
analyze and discuss the planning idea and the development of
city. While the cybercity displays some vivid pictures to users,
the designer display the designed definite photorealistic texture
to the people so they can view the designed city, Which displays
a vivid 3D city model and overcome the difference of culture
between the specialist and the clients. They are personally on
the scene when observing the nature, enjoying the scene and
knowing the entities. Based on the OpenGL graphic rendering
language, CCGIS provides the dynamic display and interactive
platform of 3D city model. By using of different detailed data and
its combination, different visual impacts are available. Such as,
the natural topographic feature can be expressed by the shading
DEM surface with coloring elevations. If DLG or DRG is wrapped
on to the surface, the exquisite spatial distribution could be clear
at a glance. If the 3D city model with photorealisitc character is
imported, then the virtual reality could be available. On the other
hand, such platform also support plenty of special display impact
like sky, cloud, color lighting, fog and annotation, walkthrough or
fly over animation, and various scenes also can be disposed
interactively very conveniently. As shown in Fig. 3, the pilot
cybercity projects are obviously attractive.
Figure 3 The pilot districts of CyberCampus and
CyberShenzhen
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