International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
application schemas and datasets, and support the storage and 
transport of application schemas and data sets. 
SVG is a language for describing two-dimensional vector and 
mixed vector/raster graphics in XML. SVG allows for three 
types objects: vector graphics, images and text. All of the objects 
transformed and composite into 
can be grouped, styled, 
previously rendered objects. It has the function of nested 
transformations, clipping paths, alpha masks, filter effects and 
template objects. Other more, SVG drawings can be interactive 
and dynamic, and it supports the DOM interface in XML. 
3. SPATIAL DATA INTEROPERABILITY AND 
VISUALIZATION BASED ON XML 
3.1 Web Service and XML Using in GIS 
There are two methods of interoperation based on XML. One is 
to exchange all data sets into the format described by XML, then 
other systems can export the data into internal schema according 
to the uniform specification; the other is real-time exporting data 
while is reading. The component for spatial data's reading, 
writing or querying is shown on XML or SOAP protocol. 
Reading spatial objects from database management system 
simultaneously, the system can export the spatial data into data 
stream defined the public interface by XML. Then other system 
can get the spatial data and query in real time. This can realize 
online data sharing and interoperation. The data stream based on 
interface of XML is ASCII code, which is easy to understand 
and realize the interoperation of the different platform. 
OGC and ISO/TC211 formulate the specification for spatial data 
interoperability based on web service/XML together, such as 
Web Map Service (WMS), Web Feature Service (WFS), Web 
Coverage Service (WCS) and Geographical information mark 
language (GML) etc. In it, WMS can make a map using the data 
with the information of Geographical space, which defining map 
as the Geographical data representation. The specification 
defines three operations: “GetCapabilities” give the server 
metadata, which is a description of the service's content and the 
necessary parameter; *GetMap" return a map which the spatial 
reference and parameter are defined; and “GetFeaturelnfo” 
(available) give the information of the special feature on the map. 
The flow of WMS is showed in Fig.l. At first, client gets the 
service metadata from GetCapabilities operation, and then client 
168 
calls the GetMap interface, puts values into the specified 
parameters, and can get a map from server. Lastly, client calls 
GetFeaturelnfo operation and gets the information of the 
appointed feature. This system realizes the WMS specification 
mainly. 
return VWMS capabilities xml document 
“Web Map. Mai 
Service 
  
1invoke GetCapabilities operation 
  
ri. 
  
2 invoke getMap operation 
  
p 
return map image(JPEG, GIF PNG,SVG) 
p; 
M 
  
3 jnvoke GetFeaturelnfo operation(toptional) 
  
HOC 
I 
return information of particular features 
eL 
Fig.1 The flow of Web Map Service 
Considering of the difference between GML and SVG, this 
paper discuss the model of interoperation and visibility of spatial 
data based on XML. For it can describe spatial object outright, 
GML is seemed as the spatial data storage and transport standard. 
But there is no common tool to show and browse the map on 
GML, it has to realize through programming which will add a lot 
of workload. SVG support the two-dimensional vector 
description, and it just need SVG viewer to brows Web Map 
page. An SVG viewer is a program, which can parse, and 
process an SVG document fragment and render the contents of 
the document onto some sort of output medium such as display 
or printer. JavaScript and Dom interface can do the complicated 
spatial operation based on SVG. 
3.2 A model of the System 
For implement the interoperability and visualization of the 
spatial data in distribute network, the system applies the 
four-layer structure on web services, which are the Database 
server, the Web Services, the Web application Server and the 
Client, shown in Fig.2. The Database server stores the data from 
different GIS platforms and has the function to exchange the 
data into the defined GML schema by the data exchanging 
components. The Web Services are according to the OGC's 
of the Web Map Service 
specification [Implementation 
Specification. Two web services function that are 
“GetCapabilities” and “GetMap” function are implemented. A 
Web Map Service produces maps of unified geo-referenced data. 
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