Geography Markup Language

1
Geography Markup Language
Milan Trninicmtrninic_at_galdosinc.com
Digital Geographic Information Working Group
Conference Vancouver, 09 April, 2003
2
Galdos Systems

• A young, fast moving software company focused on
  XML and Web-Services for Geo-spatial information
  systems
• Ron Lake, the owner and CEO was founding member
  of OGC (1993). Creator of Geography Markup
  Language.
• Lead participant in OGC standards efforts
  including GML, WFS, WCS since 1998.
• Expertise in Analysis/Design/Build, GML
  Application Schema development, XML Applications
  (XSD / XML / SVG / XSLT / SOAP / WSDL etc.), Java
  client/server side development (J2ME ? J2EE), OGC
  ISO TC/211 TC204 Standards

3
GML History

• Feb 99 White paper by Galdos on XML for
  spatial.
• Feb 99 Presentation by NTT Data
• Summer 99 Xbed Group led by Galdos Systems,
  develops SFXML (Oracle, NTT Data, MapInfo)
• October 99 Galdos Systems writes GML RFC, in
  December it becomes public
• May 2000 GML 1.0 Passed as recommendation
  paper.
• Feb 2001 OGC publishes GML 2.0
• March 2001 GML 2.0 voted as adopted
  specification
• July 2001 GML 3.0 Workshop in Vancouver
• 2001 Work on GML3.0 in progress. Work on
  harmonizing G-XML and GML3.0 in progress.
• Sept 2001 OGC votes to send GML to ISO
• 2002 Work on GML3.0 in progress
• February 2003 OGC releases GML3.0 Specification

4
GML OverviewWhat is it?

• OGC Endorsed Adopted Specification.
• A lingua franca for geographic information.
• XML technology for handling spatial data on the
  Internet.
• Emerging international standard for spatial
  dataendorsed by 200 companies and agencies
  around the world.
• Converged with G-XML (Japan) additional 600
  companies.

5
GML OverviewWhat is it?

• Data transport
• Data modeling language - build application
  vocabularies for specific domains.
• Create types for geo-spatial web service
• Data store model. Links between elements can
  exist across the Internet. Links can represent
  relationships (e.g. spatial)

6
GML Overview

• GML focuses on content and separates content and
  presentation
• GML data can be read and understood by people.
  Easily transformed.
• GML can enable distributed spatial datasets that
  are linked together local maintenance
  development /global access. Reduced cost for
  data
• GML data can easily be mixed with non-spatial
  data including text, video, and imagery.
• GML can build shareable application schemas for
  various applications like telecommunications,
  utilities, forestry, tourism, location-based
  services, etc.
• Enables creation and easy discovery of typed
  services. Provides a standard means to define
  input output arguments.
• GML is non-proprietary and open! Enables
  non-proprietary web feature servers, image/map
  annotation, map styling, spatial analysis, etc.

7
GML OverviewMajor elements of GML

• Feature model
• Geometry (2D, 2.5D, 3D)
• Topology
• Coverage
• Presentation - styling
• Coordinate Reference Systems
• Units Of Measure
• Meta data
• Dictionaries
• Temporal (moving objects)
• Observations

8
GML Feature Model

• Developed in GML2.0
• Based on OGC Abstract Specification
• Feature model of ISO 19109 matches GML (GML is a
  subset). 
• Enables complex features feature associations

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GML Feature ModelProperties
Property of a feature describes its role in the
feature
ltRadioTowergt ltpositiongt ltPointgtlt/Pointgt
lt/positiongt ltfootprintgt ltPolygongtlt/Polygon
gt lt/footprintgt ltradioCoveragegt
ltPolygongtlt/Polygongt lt/radioCoveragegt
ltnamegtKCFLlt/namegt lt/RadioTowergt
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GML Feature ModelProperties
Property value can be inline
ltpositiongt ltPoint gmlidP001gt
ltcoordinatesgtlt/coordinatesgt lt/Pointgt lt/position
gt
ltpropertygt lt/propertygt

Value
Property value can be remote
Value

ltproperty xlinkhrefhttp//.P001/gt
ltproperty xlinkhref.../gt
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GML Geometry

• ISO 19107 compliant
• 0D, 1D (linear, arcs, bezier, splines), 2D
• 2.5D Geometries (2D in 3D), 3D (solids with
  holes)
• Geometry Aggregates and Geometry Complexes

ltStreetgt ltnamegtRobsonlt/namegt ltcenterLineOfgt
ltLineString gmlidLS001 srsNameEPSG4326gt
ltcoordinatesgt49.29,-123.135
49.28,-123.115lt/coordinatesgt lt/LineStringgt
lt/centerLineOfgt lt/Streetgt
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GML Geometry
ltStreetgt ltnamegtRobsonlt/namegt ltcenterLineOfgt
ltCompositeCurve id"CC1 srsNameEPSG4326gt
ltcurveMembergt ltLineString id"C11"gt
ltcoordinatesgt gt49.29,-123.135
49.285,-123.125lt/coordinatesgt
lt/LineStringgt lt/curveMembergt
ltcurveMembergt ltLineString id"C12"gt
ltcoordinatesgt gt49.285,-123.125
49.28,-123.115lt/coordinatesgt
lt/LineStringgt lt/curveMembergt
lt/CompositeCurvegt lt/centerLineOfgt lt/Streetgt
13
GML Topology

• ISO 19107 compliant
• Nodes, Edges, Faces and Solids
• Topological complexes
• Topology can be described as a part of a feature
  or outside of features (e.g. topology of all city
  streets)

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GML Topology
ltRoute gmlidBus21Route"gt lttopoCurvePropertygt
ltTopoCurvegt ltdirectedEdge
orientation"" xlinkhref"e5"/gt
ltdirectedEdge orientation"" xlinkhref"e3"/gt
lt/TopoCurvegt lt/topoCurvePropertygt lt/Routegt
... ltNode id"n3"/gt ltNode id"n4"/gt ltEdge
id"e3"gt ltdirectedNode orientation"-"
xlinkhref"n3"/gt ltdirectedNode
orientation"" xlinkhref"n4"/gt lt/Edgegt ...
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GML Geometry and Topology
GML
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GML Coverage

• ISO 19123 compliant
• A coverage is a GML feature
• Gridded coverage, segmented curves, surface
  tessellation
• Data can be binary (file), Comma Separated Values
  (CSV), XML
• Easy to express things like distribution of
  measurement (temperature, pressure) over some
  geographic region.

17
GML Temporal Model

• ISO 19108 compliant
• Covers most of the temporal types from the ISO
  19108
• Support for dynamic feature (jointly feature and
  temporal model)
• Supports the notion of History
• Time stamping on feature or property level

18
GML Meta Data
19
GML Default Styling

• Focuses on feature styling
• Uses Scalable Vector Graphics (SVG) and Cascading
  Style Sheet 2 directly
• Capability to define styles for feature
  properties of different kinds
• Geometry styling and topology styling
• Ability to describe animation styles
• Parameterized styles the output depends on
  values of feature properties

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GML Default StylingSymbol Libraries

• Symbol Libraries created separately and used in
  GML styles

ltFeature/gt ltdefaultStylegt Inline symbol
definition using SVG and CSS2 lt/defaultStylegt
ltdefaultStyle xlinkhref.../gt lt/Featuregt
Online Symbol Library (XML)
21
GML Default Styling and SLD

• Styled Layer Description an OGC specification
• SLD has different scope describes layers and
  layer styles pertains to WMS
• GML styling mechanism describes feature styles
  can be used in any application that uses GML
• Efforts under way to harmonize GML Styling and SLD

22
GML Coordinate Reference Systems

• Emerged from work done in OGC CRS WG and GML3.0
  WG
• Complete schemas for description of all aspects
  of CRS (SRS)
• Definitions also exist for accuracy, data
  quality, units of measure etc.
• CRS defined in form of libraries and used from
  various applications, or referred to from the GML
  data directly

23
GML Coordinate Reference Systems
ltLineString gmlidLS001 srsNameEPSG4326gt
ltcoordinatesgt49.29,-123.135 49.28,-123.115lt/coord
inatesgt lt/LineStringgt
Online CRS Registry
ltgmlGeographicCRS gmlid"urnepsgv6.1crs4326
"gt ltogcdataSourcegtEPSGlt/ogcdataSourcegt
ltogcrevisionDategt6/2/1995lt/ogcrevisionDategt
ltgmlnamegtWGS 84lt/gmlnamegt ltgmlscopegtUsed by
the GPS satellite navigation system and for NATO
military geodetic surveying.lt/gmlscopegt
ltgmlusesCoordinateSystem xlinkhref"urnepsgv6
.1cs6402"/gt ltgmlusesDatum xlinkhref"urneps
gv6.1datum6326"/gt lt/gmlGeographicCRSgt
24
GML and ISO

• GML 3.0 is the baseline for ISO GML.
• We do not expect major changes in GML in order
  for GML to become an ISO specification (ISO
  19136)
• There are no serious compliance issues - a joint
  meeting (ISO and OGC) was held in Annapolis and
  this was discussed at length
• OGC and ISO have agreed to create an integrated
  task force and produce a single specification
• Joint task force to meet in May and likely also
  in Vancouver in July. 
• We anticipate GML will be an ISO DIS by Dec 2003
  or Jan 2004.

25
GML Performance
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GML Applications
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GML Future
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GML Notes

• GML Dev Days in Vancouver, July 2003
• First book on GML GML Guide presently in print