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RESEARCH ON THE THREE-DIMENSIONAL ABSTRACTION AND DESCRIPTION OF 
REALITY 
LI Chengming®, WANG Jizhou®, Lin Zongjian" 
“Institute of GIS, Chinese Academy of Surveying and Mapping, No.16, Road Beitaiping, District Haidian, Beijing, P.R.China, 
100039, E-mail: emli@casm.ac.en, wangl16642163.net 
* Chinese Academy of Surveying and Mapping, No.16, Road Beitaiping, District Haidian, Beijing, P.R.China, 100039, 
E-mail: casm@casm.ac.cn 
KEY WORDS: Abstraction, Building, Database, City, Reconstruction 
ABSTRACT: 
The method of how to abstract reality into a two-dimensional map is already mature, but with the development of three-dimensional 
GIS, we have to be up against the problem how to describe the reality in a 3D means. Although there are already many 3D GIS 
software and systems from various corporations, the standard for 3D abstraction and description of real world is still poor. In the 
paper we have done some elementary research on this issue, we think that there are three key matters which should be implemented 
including Description Contents, Abstraction Method and Expression Model. And according to the above, we put forward several new 
concepts and methods that are 3D Geographic Element System, Spatial Granularity for 3D Description (3DSG), 3D Partition of 
Building and Model Databases of City. In 3D Geographic Element System we define ten kinds of abstract elements to express the 
reality. 3DSG is used to confirm the subtle degree that we describe the real world and acquire 3D spatial data, and we put forward 
four principles to estimate 3DSG which are application integrated, applicable, practicable and regional. Buildings are the main sites 
that humans perform their daily activities, and are difficult to describe for the complex structures, so we bring a partition method to 
implement accurate expression of buildings. By 3D Partition we divide a building into three parts: Mainbody, Character and Adjunct. 
SA SE 
Model Databases of City is used to realize the efficient reconstruction of city, and it is composed of Building Character Database, 
Building Texture Database, Ground Texture Database and Independent Object Database. 
1. INTRODUCTION 
Since the birth of the people, they have never stopped exploring 
the living environment in order to improve their adaptability to 
the reality. Mature abstraction and description of reality is 
essential to distribute the existing knowledge and advance the 
sciential level of the whole people. In the different periods of 
human evolvement, limited by the science and technology 
developing level, there are various means that people used to 
abstract and describe the world, such as language, character, 
graph, table and map. Among these means, map played a very 
important role. Using intuitionistic symbol and exact position, 
map gives a comparatively detailed description of reality, and 
has been used in all kind of fields. But in nature map is a 
projection from the three-dimensional world to a two- 
dimensional plane, so there is a great loss of the side 
information. At the same time a good deal of abstraction, 
generalization and synthesization arc used in cartography, and 
thus there are limitations of information transmission in a 
certain degree. With the development of related technologies, it 
is possible to express the world vividly in a three-dimensional 
means, either physical or digital. To reconstruct a three- 
dimensional world, many corporations produced their own 
software and systems, but there is still lack of the standard for 
3D abstraction and description of real world. 
The world is composed of various things which have different 
modes, states and attributes, and it is unpractical and 
unnecessary to describe and express them in a way the same as 
the realistic prototypes. So experts in different application 
domains determine the contents, types and hiberarchy of 
description according to their own actual demands. For example, 
in the domain of city management, the emphases are put on 
describing the surface things including buildings, streets, 
crossroads, terrain and so on; but in the domain of mine and 
geology, the research objects are located under the ground, and 
geology, mineral resources and rocks are absolutely necessary 
elements. Therefore, it is nessary to develop different 3D 
description and expression standards aiming at different 
application fields. City, as an important habitat where people 
perform their daily activities, is a main site which civilization is 
created, developed and distributed. Accurate 3D reconstruction 
of the city based on geographic information technology can 
provide not only scientific support to make decision for a lot of 
national departments, but also information service for public. In 
the following paper we do some elementary research on how to 
realize three-dimensional description and expression of city. 
The paper thinks that there are three key matters which should 
be implemented including Description Contents, Abstraction 
Method and Expression Model. And accordingly the paper put 
forward 3D Geographic Element System, Spatial Granularity 
for 3D Description, 3D Partition of Building and Model 
Databases of City, and tested the efficiency through practice. 
2. 3D GEOGRAPHIC ELEMENT SYSTEM 
In order to realize 3D expression of city, the first problem is 
about description contents, that is, to construct geographic 
element system of 3D expression of city. With many years 
development of cartography, it has become mature and founded 
a graphic element system which consists of habitation, water 
system, traffic feature, ambit, terrain and physiognomy, 
vegetation and so on. It has been proved that these elements can 
meet a majority of users’ need to a certain extent through many