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Implementation of Vector Markup Language for Cartographic Data Applications

Michael Gould

Lecturer in Computer Systems and Languages

Universitat Jaume I Escuela Superior de Tecnologia y Ciencias Experimentales (ESTCE)
Castellon Valencia Spain E-12071
Phone: +34 964 72 83 17
Fax: +34 964 72 84 35
Email: gould@uji.es Web: http://arcoiris.act.uji.es

Biographical notice:

Michael Gould is a specialist in GIS (Geographic Information Systems) and has worked in industry, academia and as independent consultant. He has been principal investigator on several European Community-funded projects, and is currently involved in constructing the European Spatial Metadata Infrastructure (http://esmi.geodan.nl/ ) using distributed platforms. His computer graphics laboratory is a founding member of AGILE (Association of Geographic Information Laboratories in Europe) and associate member of the OpenGIS Consortium (http://www.opengis.org ). More information may be found at (http://www.lander.es/~mgould/ ) and at (http://arcoiris.act.uji.es/ ).

Ribalaygua, Antonio
Santander

Spain

XYZ Sistemas Industriales, S.A.

Antonio Ribalaygua

Director

XYZ Sistemas Industriales, S.A. Avenida Los Infantes, 105
Santander Cantabria Spain E-39005
Phone: +34 942 272 791
Email: arb@imapper.com Web: www.imapper.com

Biographical notice:

Antonio Ribalaygua has been a software engineer for 12 years, mainly in the fields of CAD and digital cartographic data. In 1992 he founded the software firm XYZ Sistemas Industriales, S.A. He is a registered MSDN ISV developer and he recently created the world's first map server based on VML (Vector Markup Language) , accessible at (http://www.imapper.com ).

ABSTRACT:

VML

cartography

graphics

The geographic information community -consisting of data producers, geographic information system vendors, researchers and end users- has been reaping benefits from the strong growth in web technology markets, primarily because the web assists in disseminating geoinformation to a much wider audience than has been possible during the roughly 40-year history of the creation and use of digital geographic information, comprised of digital maps, satellite imagery, census and other socioeconomic data related to places on the earth. Despite a myriad of technological advances, however, this community still faces a major barrier to the open dissemination of geographic information -which is largely created and maintained by government authorities- primarily due to incompatibility of data formats and the lack of metadata associated with much of the GI currently available. On the implementation side, most map servers on the web serve static bitmaps, and the few which serve vector graphics normally use proprietary formats and require plug-in software in order to view their map formats. These elements together frustrate the interoperability and data sharing process. Meanwhile, the W3C (World Wide Web Consortium) recently formed a working group dedicated to open vector graphic formats for the web, and this group subsequently published a Scalable Vector Graphics Requirements working draft (http://www.w3.org/TR/WD-SVG/ ) on February 11, 1999. Applications or profiles of Scalable Vector Graphics promise to provide flexible solutions to the problems previously mentioned, primarily thanks to their encoding of graphic elements in XML 1.0 format. Although SVG is, at the time of this writing, still a draft specification and cannot yet be edited or viewed, a prototype SVG-compliant language called Vector Markup Language became available in November 1998 within the beta versions of Microsoft products Office2000 and Internet Explorer 5. In order to test the capabilities of VML for cartographic data provision a VML-compatible map server was developed by the second author. On-going testing indicates that VML, and by extension we assume SVG, is a more than viable option for the sharing of cartographic data, in both vector and bitmap formats, and furthermore we expect SVG to become a de facto standard for web-based geographic information systems during the coming years. Finally, the authors solicit collaboration with third parties in our continuing dvelopment and testing.

Introduction

cartography

geographic

The field ofgeographic information technologies , also known as GIS, is growing at an astonishing rate as many businesses begin to recognize the value of the spatial dimension of their vast databases. Proof of this growth may be found in the recent entrance into the GIS market of IT giants Microsoft, Oracle and Autodesk, just to name a few. While the technology side of the GIS puzzle is more or less complete -it evolves smoothly alongside other IT markets- a major barrier to the massive diffusion of geographic technologies is the poor availablity of geographic data, which normally is not user-defined such as in CAD or desktop publishing, but rather collected and stored centrally by government agencies and large earth-observation satellite companies. The investment is so great in this data collection effort that monopolistic practices often prevent the easy flow of these data, into the hands of value-added resellers for example. This situation is extremely more pronounced in Europe in comparison with the USA. Proprietary data formats also abound, which limits severely the interoperability of heterogeneous geographic techologies. In an attempt to counter these problems the OpenGIS Consortium (http://www.w3.org/TR/WD-SVG/ ) was formed in 1994, as an industry lobby and technology specifications definition group. Curiously, however, while OpenGIS has been hard at work defining open systems standards based on complex services/interfaces such as Corba and SQL, the web community has evolved to such an extent that today much of what OpenGIS proposes can be accomplished via the judicious application of XML and ordinary HTTP server technologies. The recent appearance on the WWW scene of 2-dimensional vector graphic elements defined as XML tags, is perhaps the most important example of this trend, from the perspective of the geoinformation community.

SVG

graphics

Scalable Vector Graphics

The Scalable Vector Graphics specification under development by the Vector Graphics Working Group of the W3C promises to resolve several of the problems mentioned in the previous section, mainly with regard to data accessibility and interchange. The objective here is not to enter into the details of the specification, for which the working draft may be consulted at: (http://www.w3.org/TR/WD-SVG/ , rather to suggest that interactive cartographic applications serve as an ideal reference for testing the capabilities of an emerging vector graphics format such as SVG.

It is important to underscore the fact that at the time of this writing no SVG-compatible clients are available, and so our discussion of the specification and its applications remains just that: a discussion. But this is not to say that we are unable to test similar specifications and extrapolate our findings to the future capabilities of SVG version 1.0. In May 1998 a consortium of several key IT companies including Autodesk and Microsoft, submitted a proposal for W3C recommendation of its Vector Markup Language (VML). To provide context we should recall that at this time there existed a sort of vacuum in the 2-D vector graphics domain, when although Macromedia'sFlash and variants of CGM existed they were not XML-based (text) solutions. Therefore, the authors quickly adopted VML, also because it was from the start rather well documented and because it becameusable in November 1998 with the release of the Internet Explorer 5 beta 2 browser. By December 1998 the second author had put on-line theInternet Mapper VML map server at (http://www.w3.org/TR/WD-SVG/ .

VML	Implementation of Vector Markup Language

The present version of the Scalable Vector Graphics specification incorporates positive attributes from prototype VML and Precision Graphics Markup Language (PGML) formats. Therefore, we are able to indirectly test some of the future functionality of SVG by implementing a VML-compatible server.

Some of the advantages of the VML-based map server over present bitmap servers include:

XML format allows users to access and manipulate map data;
it does not rely on plug-in software;
it it is scalable and styleable; and
it allows for interaction with individual graphic elements (i.e. segments, icons).

Sample maps in VML

The Internet Mapper VML server demonstration web pages include the map pictured in figure 1, of the city of Santander on Spain's northern coast. The map is composed on closed polygons to represent city blocks, icon files hyperlinked to web pages, and active line segments along street centrelines. The application includes attribute data storage via links to Access-format files and ODBC connections.

Tourist-style map of the city of Santander, rendered in native VML.

The VML code is not protected from the user, and is revealed using the Show Source option. Following is a snipet of the VML code used to create the Santander map.

<v:group style='position: absolute; left:0; top:0; width: 600px;
height: 350px; clip: rect(auto, auto, auto, auto);
' coordsize=600,350 coordorigin="0,0">
<v:polyline points="10 105 60 124 140 154 138 158 58 128 8 109"
title="Calle Juan de Herrera"
href="  fill="true" strokecolor=#FFFFFF strokeweight="1px">
</v:polyline>
<v:polyline points="3 122 52 143 101 162 136 173
134 177 99 166 50 147 1 126" title="Calle San Francisco"
href="  fill="true" strokecolor=#FFFFFF strokeweight="1px">
</v:polyline>
<v:polyline points="-10 143 43 170 86 186 153 206
151 210 84 190 41 174 -12 147" title="Avenida Calvo Sotelo"
href="  fill="true" strokecolor=#FFFFFF strokeweight="1px">
</v:polyline>
<v:image style='position: absolute; left:585; top:165;
width: 16; height: 16;' src="cruzroja.gif"
title="Sanatorio Madrazo" Id="sanamadr" href="imsql.asp?
Id=sanamadr&Layer=Centro_medico&
Label=Sanatorio_Madrazo" target=
"_parent"></v:image>

One of the key features in VML, also carried over to SVG, is the ability to transform coordinate systems from real-world spaces (respresented in units such as kilometres or degrees of latitude) to local user spaces. This facilitates the import or direct visualization of cartographic data sets from a variety of sources. Also supported, though not without bugs, are viewports and zooms.

Another key feature of VML is that it is the native graphic format of the Office2000 suite of office automation applications now being beta-tested by Microsoft. (See, for example, the Santander map within a Word2000 document, in figure 2.) This essentially means that quite soon millions of Office users will possess VML creation capability. Graphics may be drawn directly within a Word2000 document, and then 'saved as' a web document. In the process Word 2000 does two things: it creates a folder called file-name_files, which contains not only the VML codes but also a duplicate GIF image of the graphic. Later, when we open the graphic within the IE 5.0 browser, it appears in its native VML format. If, however, we open the graphic in Netscape Navigator, then the GIF version appears. While the two versions look alike, we know that the IE 5 version (VML) may be openned (using the View Source option) and edited, either by hand or, ideally, via any common scripting language. This the behavior which the geographic information community is seeking, and we expect that SVG applications will allow us this level of interactivity and access, and much more.

The Santander map within a Word2000 document.

Future work

The next step in the testing and implementation process will naturally be to either acquire or develop SVG-format clients, and to further exploit the interactive and object-oriented aspects of SVG. Also under way is the development of dynamic interfaces to the Internet Mapper server, utilising DHTML scripting. Increased access to the attribute database associated with individual graphic elements using pure XML-based solutions will also be a priority, in order to relieve users of the need to store these data in Access or other relational data managers. Additionally, the VML server is being applied to build a university campus guide web site, at the first author's campus (see figure 3).

An application of Internet Mapper as a university campus guide.

Finally, the authors openly welcome collaboration by third parties who share an interest in these cartographic applications of SVG and in XML in general.

Bibliography

Gould-Rib 00: Gould, M. and Ribalaygua, A., SVG: A new breed of vector graphics for the web, GeoWorld 12(3), pp. 46-48. 0000


International Standards for document description and processing		Table of contents		Indexes		EXPERTS (EDI/XML Procurement Enabling Real Trade Standards)