Full text: The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics

ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS’’, Bangkok, May 23-25, 2001 
320 
GEOD2D: A FLEXIBLE SOLUTION FOR GIS DATA EXCHANGE BASED ON COM 
Huayi WU 12 Xinyan ZHU 2 
1 School of Business, Hubei University, Wuhan, 430062, China, wuhy@public.wh,hb,cn 
2 Resarch Center for GIS, Wuhan University, Wuhan, 430079, China, zxv@rcgis.wtusm.edu ; _cn 
KEYWORDS Data Exchange, COM/DCOM, ActiveX/OLE 
ABSTRACT 
This paper introduces our experiences of developing a flexible solution for GIS data exchange system based on COM. A series of 
ActiveX Controls were developed for assembling various data exchange applications among GISs. Our experiences verified that 
COM/DCOM model is a flexible and economic solution for GIS data exchange. 
1. BACKGROUND 
Data preparation is one of the hardest tasks in making a GIS 
practicable. It is estimated that more than 80 percentages of a 
GIS project is collecting, coordinating, inspecting and input data 
into the GIS database. Generally, commercial GIS software 
packages provide menu items to fulfill data exchange between 
various data formats. But these menu items often fail to meet the 
needs of various end users of GIS software. There are several 
causes prevent the success of import and export data from GIS 
to GIS or other graphic systems. 
The data models are not identical between GISs or GIS 
and other graphic systems. A typical example is the data 
model of CAD, which is severely different from that of 
usual GIS. Many entities in CAD have no counterparts in 
GIS. 
^ The user’s need for GIS varies from one user to another. 
Urban planning department has its own convention that is 
thoroughly different from that of surveying and mapping 
department. An inflexible solution can not meet these two 
kinds of different need simultaneously. 
GIS solution providers also try to overcome these 
problems. They provide many options for end user in the 
data exchange menu items. These options in a certain 
extend offer variable solution for end users, but it is far 
from all needs of end users. 
^ For GIS solution providers, another effort is made the data 
standard. The OpenGIS consortium is an example. 
Theoretically it is not difficult to abide by the OpenGIS 
specification, but it is not rational to require a GIS 
constructor to have all its data sets follow the OpenGIS 
specification, especially those historically accumulated 
data. 
For GIS software developer, another puzzle is to keep 
pace of the upgrading step of other graphic systems and 
their data formats. 
To solve all above problems, COM is an economic and flexible 
solution. Our successful experience verified this selection. 
2. COM/DCOM MODEL OF ActiveX TEHNIQUE 
With the achievement of computer software engineering, the 
component technique is promptly applied to design GIS. 
Component GIS is designed to base itself on a series of 
standard components. Some of these components are imported 
from commercial providers. Others are developed specially for 
spatial information. The most important feature of these 
components is the flexibility of being rearranged into customized 
system. Visual and standard interface makes these 
customizations an easy and convenient building block to 
construct a new system for end users. 
Currently there are two mainstream models for developing 
component system. One is Microsoft Component Object Model 
(COM) and Distributed COM (DCOM). Another is OMG’s 
Common Object Request Broker Architecture (COBRA). 
Microsoft’s power position makes COM/DCOM the more popular 
model to develop components. Incorporating the spreading of 
COM/DCOM model, Microsoft released the ActiveX technique 
and a series of supporting tools for designing, coding, debugging 
and testing ActiveX components. ActiveX component is in 
practice the most wide-adapted standard component for visual 
programming. In the present stage, Component GISs are mostly 
ActiveX components or its predecessor OLE components. This 
paper will introduce our experiences of developing a series of 
ActiveX components for GIS data exchanging. 
ActiveX is a set of open techniques based on COM/DCOM. It 
stands for a strategy of integrating application system and 
Internet. No matter what language is utilized to develop an 
ActiveX component, components abiding by this standard 
support interoperation in PC or distributed environment. 
There are three types of ActiveX component for common use. 
They are Control, automation Server and Document. As a 
reusable component, ActiveX Control appears an encapsulated 
code block. It provides Attributes (member variables), Functions 
and Events for communication with other programs. ActiveX 
control is also a special OLE Control. It can be used not only in 
container that supports OLE, but also as an Internet Control to 
become part of web pages. ActiveX Control can be developed in 
various language environments such as VB, VC etc. ActiveX 
Control can be imported to various language environments, such 
as VB, VC, Delphi, PB, VF etc., to incorporate the development 
of application systems. 
In this paper, VC++ is chosen to develop ActiveX Controls and 
VB is chosen to test these ActiveX Controls with an experimental 
system. Experiments of these components called by Delphi and 
PB was also conducted with satisfactory results. 
3. DESIGN OF DATA EXCHANGE 
COMPONENTS FOR GIS 
Among GIS users, there are about ten data formats frequently 
used. Some famous of them are DWG, DXF, MIF, Coverage, 
SHAPE etc. Traditionally, to provide a total solution for data 
exchange among them, it is required to work out an executable 
program for each pair of them. Designed by ActiveX technique, 
what we have to do is to work out a series of ActiveX Controls 
and customize them to final applications. 
In our experiments, one component is designed for each type of 
data format. For example, an ActiveX Control GeoDXF is 
developed for dxf format and so is an ActiveX Control GeoVCT 
for China's standard spatial data exchange format VCT. Each of
	        
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