ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001 
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A NEW APPROACH FOR DISTRIBUTED GIS 
Yuxiang WANG, Chongjun YANG, Donglin LIU 
China Beijing 100101 
Institute of Remote sense Application, Chinese Academy Sciences 
KEYWORDS: Distributed GIS, CORBA, ORB, Geo-Spatial Data 
ABSTRACT 
The research described in this paper explores a new approach towards distributing GIS tools across multiple CORBA ORBs. The main 
structure of a distributed GIS is introduced. How CORBA and GML are integrated is explained. Object migration is implemented among 
servers for load balance and security is considered. Then the main procedure of designing a CORBA distributed GIS is introduced. 
1. INTRODUCTION 
GIS has become an indispensable spatial data processing tool 
for government and research. With strengths in reliability, 
processing efficiency, resource sharing, parallel processing and 
system scalability. A distributed GIS is a collection of GIS sites. 
Each site is an autonomous GIS that contains both 
geo-processing and spatial data. It is a group of physically 
distributed GIS sites. They are logically united as one site. For 
user, geographic service can be accessed transparently. 
• Compared with a centralized-server GIS, the major 
advantages of a distributed GIS are as follows: 
• Evenly load balance can be achieved by strong 
multiple GIS sites. When a site works wrong, other 
sites will finish the process left. 
• High speed can be achieved by distributing the whole 
job to multiple sites for parallel processing. 
• Data and processing interoperability are enhanced and 
system development cost is reduced. 
• In a well-planed distributed GIS, system is easily 
scalable. 
A distributed GIS has advantages in data sharing, reliability and 
system growth. In recent years, distributed GISs have attracted 
increasing interest. For examples, the Distributed Geographic 
Information System Project in Australia and in Norway, and the 
geodata modeling technique for distributed GISs at Berkley. The 
National Center of Geographic Information Analysis(NCGIA) 
includes distributed GIS in its research plan. The University 
Consortium for Geographic Information Science included 
distributed computing and interoperability in its research 
priorities. 
2. CORBA BRIEF 
The Common Object Request Broker Architecture (CORBA) is 
made up of Object Request Brokers (ORBS) that can 
communicate with each other via the General Inter-ORB 
Protocol (GIOP), the Internet Inter-ORB (HOP) Protocol [2]. 
CORBA facilitates a middle-tier, object-to-object infrastructure 
that allows one to encapsulate data from multiple sources. The 
language and compiler used to create the server objects, as well 
as the location of distributed CORBA objects and the operating 
system they execute on, are totally transparent to clients. 
CORBA therefore provides an ideal mechanism for creating 
3-tier (or n-tier) distributed applications that go beyond providing 
simple interoperability [2]. 
CORBA provides one with ability to perform dynamic discovery 
of objects and services, as CORBA objects are self-describing 
and introspective. CORBA's dynamic facilities, including 
Dynamic Invocation Interface (Dll), and the Interface Repository 
allow the creation of extremely flexible systems that allow 
run-time discovery and late-binding [2]. This is especially useful 
in the Web environment where a user is able to discover new 
services and then make use of them transparently. 
3. DISTRIBUTED GIS MODEL WITH CORBA 
Distributed GIS is based on a distributed geospatial database. 
Clients can access GIS server remotely and concurrently. The 
whole structure of our distributed GIS is showed (Fig.1). 
Because our distributed web GIS servers include many functions, 
we divide our GIS functions into different ORBs. They are 
projection Transform ORB, Data Format Transform ORB, Spatial 
Database Storage ORB, Spatial Index ORB and Application 
ORBS (Fig 2). All the CORBA objects are communicated by HOP 
protocol. They are located and managed by Naming Service and 
Interface Repository. The naming service locates data objects by 
name. Each data object, for example, a digital map or a remote 
sense image, has a descriptive, recognizable name used for 
query. The naming service maps the name into the address and 
the reference of the object. 
Fig 1 : Distributed GIS Architecher