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Introduction to GML (Geography Markup Language) as a tool to exchange geographic data

Introduction to GML (Geography Markup Language) as a tool to exchange geographic data. David Sol, Professor - Researcher, UDLA Antonio Razo, Research Assistan t , UDLA Tel: + 52 ( 222 ) -229 2 0 29 Fax: + 52 ( 222)-229 21 38 Email: sol@mail.udlap.mx, anrazo@mail.udlap.mx.

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Introduction to GML (Geography Markup Language) as a tool to exchange geographic data

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  1. Introduction to GML (Geography Markup Language) as a tool to exchange geographic data David Sol, Professor - Researcher, UDLA Antonio Razo, Research Assistant, UDLA Tel: +52 (222)-229 2029 Fax: +52 (222)-229 21 38 Email: sol@mail.udlap.mx,anrazo@mail.udlap.mx

  2. Geo-Information Technologies Lab Center for Research in Information and Automation Technologies CENTIA – UDLA-P http://www.udlap.mx/~gisudla gisudla@mail.udlap.mx +52 (222) 2-29-20-29

  3. Instructors David Ricardo Sol Martinez is director of the Computer Systems Engineering Department at Universidad de las Americas Puebla (UDLA-P),Mexico. He holds a PhD. degree in Information Science from the Universite de Savoie in France, and a B.Eng. degree in Computer Systems Engineering from UDLA-P. Since 1998, he works as a Professor of the Computer Systems Engineering Department at UDLA-P. He also heads the Laboratory of Geo-Information Technologies from the Center for Research in Information and Automation Technologies (CENTIA) at his university. His main research interests lie in the areas of Geographic Databases. He has worked in several projects supported by the National Council of Science and Technology (CONACYT) of Mexico and has directed several Master and Bachelor theses. Antonio Felipe Razo Rodriguezworks as a research assistant at the Laboratory of Geo-Information Technologies from the CENTIA at UDLA-P. He holds MSc. degree in Computer Science and aB.Eng. degree in Computer Systems Engineering from UDLA-P. His subjects of research involvesthe use of XML, 3D and OpenGis specifications for Geographic Databases.

  4. References • World Wide Web Consortium (XML,SVG,XSLT) • www.w3.org • OpenGis Consortium (GML) • www.opengis.org • European Petroleum Survey Group EPSG(SRS) • www.ihsenergy.com/epsg/epsg.html • Web 3D Consortium (VRML, GeoVRML) • www.vrml.org

  5. Overview • GMLIntroduction • GML in action • GML in detail • GML future

  6. Geography Markup Language Introduction

  7. Introduction • ...for the first time spatial information have a truly public encoding standard, GML...it will revolutionize the treatment of spatial information Ron Lake, Galdos Systems, Inc.

  8. GML topics include • map making • data transformations • spatial queries • geographic analysis • GML-based spatial databases • GML applications for mobile computing systems, web feature services...

  9. What is GML ? • GML or Geography Markup Language is an XML based encoding standard for geographic information

  10. Definition • The Geography Markup Language (GML) is an XML encoding for the transport and storage of geographic information, including both the geometry and properties of geographic features

  11. GML is a Recommendation • OpenGIS® Consortium Recommendation Paper • OGC Document Number: 00-029 • Date: 12-May-2000

  12. GML specification • ...this specification defines the mechanisms and syntax that GML uses to encode geographic information in XML...

  13. GML specification • ... GML will make a significant impact on the ability of organizations to share geographic information with one another, and to enable linked geographic datasets...

  14. GML specification • ...the initial release of this specification is concerned with the XML encoding of what the OpenGIS® Consortium (OCG) calls ‘Simple Features’...

  15. What is OpenGIS ? • www.opengis.org • International Consortium • over 220 members • Universities, Government Agencies, Companies • MIT, Harvard, NASA, FEMA, ESRI, MapInfo, Oracle, Galdos Systems Inc

  16. Geographic data • geographic data vs. graphic interpretation • When we talk about geographic data we are trying to capture information about the properties and geometry of the objects which populate the world

  17. GML is XML • Just as XML is now helping the Web to clearly separate content from presentation, GML will do the same in the world of geography

  18. Graphic interpretation • When we talk about graphic interpretations of that data we are talking about a map or other form of visualization. How we symbolize data on a map, colors or line weights • A GML document is not a Map !

  19. GML and Maps • To make a map from GML we need to style the GML elements into a form that can be interpreted for graphical display in a web browser ( or any other device )

  20. GML and Maps • Potential graphical display formats include W3C Scalable Vector Graphics (SVG), the Microsoft Vector Markup Language (VML), and the X3D • Image formats as well; png, gif, jpeg, pdf

  21. GML is Text • GML represents geographic information in the form of text • Text is easy to create, read (inspect),modify, transport and to store • human and machine readable

  22. GML • Encodes Feature Geometry and Properties • Based on the Abstract Model of Geography developed by the OGC that describes the world in terms of geographic entities called features. • Essentially a feature is nothing more than a list of properties and geometries

  23. Properties • Properties have • name • type • value • description

  24. Geometry • Geometries are composed of basic geometry building blocks such as • points • lines • curves • surfaces • and polygons

  25. For example • To model a school • Properties • Name – text • Description - text • Id - number • Level - text • Geometry • locationOf • Point

  26. GML Geometry • For simplicity, the initial GML specification is restricted to 2D geometry, however, extensions will appear shortly which will handle 2 1/2 and 3D geometry, as well as topological relationships between features.

  27. GML Geometry • GML encoding already allows for quite complex features. The geometry of a geographic feature can also be composed of many geometry elements. • A simple feature such as a radio transmission tower may have a point property (its location), and an area (multi-polygon) property which is its coverage zone

  28. Spatial Reference Systems • An essential component of a geographic system is a means of referencing the geographic features to the earth's surface or to some structure related to the earth's surface • GML incorporates earth based spatial reference system which is extensible and which incorporates the main projection and geocentric reference frames in use today by the European Petroleum Survey Group (EPSG)

  29. Why encode a spatial reference system ? • Client validation of a server specified Spatial Reference System • A Coordinate Transformation Service can compare the SRS description with its own specifications to see if the SRS is consistent with the selected transformation • To control automated coordinate transformation by supplying input and output reference system names and argument values

  30. GML Feature Collections • The XML 1.0 Recommendation from the W3C is based on the notion of a document • The current version of GML is based on XML 1.0 and uses a FeatureCollection as the basis of its document

  31. GML Feature Collections • A FeatureCollection is a collection of GML Features together with a bounding Box element (which bounds the set of Features) • A FeatureCollection can also contain other FeatureCollections, provided that thebounding Box of the boundingFeatureCollection bounds the bounding Box of all of the contained FeatureCollections

  32. GML - More than a Data Transport • GML is an effective means for transporting geographic information from one place to another • But it will also become an important means of storing geographic information forbuilding complex and distributedgeographic data sets

  33. Objectives of GML • If it is implemented as a Standard Format • data could be developed on the local scale and readily integrated to the regional and the global scale • If it is implemented for Specific Applications • data developed for one purpose could be readily integrated with data developed for another

  34. Overview • GMLIntroduction • GML in action • GML in detail • GML future

  35. Geography Markup Language GML in action

  36. Our experience Geo-Information Technologies Laboratory http://www.udlap.mx/~gisudla • Working with OpenGis standards for 4 years • Working with GML for 2 years

  37. Presentations • “Standard 2D and 3D geo-spatial data formats” Encuentro Nacional de Computación 2001 • “GISELA: A web-based interface using XML and open standards” Vancouver GML Dev Days July 22nd-26th, 2002 • “GML: Compartición de Datos Geográficos”Conferencia Latinoamericana de usuarios de ESRI y ERDAS 2002

  38. Current Proyects • GISELA X3-X2 • A web-based interface using XML and open standards, HTML-SVG-X3D • GeometaX • Metadata geographic standards using XML • PocketGIS • XML-based mobile information system

  39. GISELA X3-X2 Geo database GML GML DBF SHP XSLT VRML HTML X3D XSLT SVG

  40. GeometaX

  41. PocketGIS Server PDA

  42. Sources • Digital Cartography • ArcView • Spatial Analyst • 3D Analyst

  43. Generating GML • Avenue Script • ExportGML.ave 'Fecha: 10 de Diciembre de 2001 'Modificado: 15 de Agosto de 2002 'Autor: Laboratorio de Tecnologías de Geoinformación (XALTAL) ' CENTIA - Universidad de las Americas-Puebla ' Ing. Antonio Razo Rodriguez 'Nombre: ExportGML.ave 'Version: 0.73 'Exporta los puntos de puntos, polilineas y poligonos en 2D y 3D 'ademas copia sus atributos descriptivos a un archivo con la extensión .xml 'de acuerdo a la especificacion del Geography Markup Language v 1.0 'del OpenGis Consortium (www.opengis.org) '- Actualizado para exportar multipoligonos y poligonos con huecos '- Actualizado para exportar bounding box con los elementos seleccionados 18/07/02 '- Actualizado para exportar MultiPoint (falta MultiPointZ ) 15/08/02 '- Actualizado para exportar MultiLineString (falta MultiLineStringZ ) 15/08/02 '- Corregido error de MultiLineString 29/08/02

  44. File Header Record Header Record Header Record Header Record Header Record Contents Record Contents Record Contents Record Contents Generating GML • Java program • Shapefile binary format to GML • Shapefile Technical Description [http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf] • Shape • 0Null Shape • 1Point • 3 Polyline • 5 Polygon • 8 MultiPoint

  45. Database • GMLReader to OpenGIS SQL • ShapefileReader to OpenGIS SQL Input Output Geo database GML GML Features Layers Features Layers Server Client Client

  46. Functionality HTML SVG GML XSLT X3D

  47. XSL Stylesheets • GML2SVG • GML2VRML2D • GML2VRML3D

  48. Overview • GMLIntroduction • GML in action • GML in detail • GML future

  49. Geography Markup Language GML in detail

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