the open planning project
Open Source GML
Tools and Usage
the open planning project
Overview
• Quick Background
– Organizational biases, GML products
• Existing Open Source Tools
– Libraries
– Generation
– Consumption
• Unresolved Issues
• Conclusions
– What should you use?
the open planning project
TOPP
• Previously Vision for New York
• Mission:
– Develop open source digital earth tools
– Demonstrate technology projects
– Advocate for open, free geographic information
• Software Products
– GeoServer (Geographic Server)
– Virtual Terrain Project (Visual Simulation Client)
• GML is core to our products
– Java bias
the open planning project
Product: GeoServer
– J2EE
– Full nontransactional WFS
– Reads from
PostGIS
– Full transactional
support
the open planning project
Product: Virtual Terrain
– C++/OpenGL
– Latest build has
WFS import
support for
generic objects
– Cultural objects
transitioning to
GML encodings
– Working on full
run-time WFS
compatability
the open planning project
Open Source GML Libraries
• Java
– GML4J (Galdos)
– GeoTools (Leeds/TOPP)
– OpenMap (BBN)
– Geobject? (Polexis)
• C++
– OGR (Warnerdam)
• Other Languages
–?
the open planning project
Case Study: GML4j
• Approach
– DOM Parser (tree structure)
– Tools to walk tree structure
• Advantages
– Most general parser
• Disadvantages
– Memory intensive and slow (DOM)
– Thin feature framework
the open planning project
Case Study: GeoTools2
• Approach
– SAX parser (event-based)
– Directly transformed to internal feature model
• Advantages
– Fast and low-memory
– Rich toolkit available
• Disadvantages
– Loose generality and flexibility with features
– Toolkit somewhat immature
the open planning project
Open Source Generators
• GeoServer
– Known to have interoperated
• Academic
– UMN MapServ (planned)
– Other academic projects
• Nothing packaged
• Commercial
– Under a dozen
the open planning project
Open Source GML Viewers
• Virtual Terrain Project (TOPP)
– Beta support via OGR
– All internal storage to GML
• SVG Viewer
– Javascript-based
– Nedjo Rogers talk tommorrow
• MapServer (UMN), GeoServer (TOPP)
– WMS viewing support coming
• Non-Productized Viewers
– GeoTools, OpenMap
the open planning project
Open Issues
• Base Issue
– Dealing with the complexity of GML features
• Overview
– Feature Type Complexity
– Internal Feature Types
– Schema Proliferation
– Projections
the open planning project
Issue: Feature Type Complexity
• Issue
– Structure and syntax complex
– Post-GML, interoperability remains elusive
• Proposals
– ESRI’s Simple GML proposal
– Warnerdam
• Conclusions
– Adhere to flat feature schemas
the open planning project
Issue: Internal Feature Types
• Issue
– Tightness of coupling
– Tradeoff: power vs. flexibility
• Approaches
– Generic Models: GeoTools2
– Simple Models: OGR
• Conclusions
– Simple features will dominate toolkits
the open planning project
Issue: Schema Proliferation
• Issue
– Representation for common objects
• Proposals
– Information Communities (OGC)
– SEDRIS (MITRE)
• Conclusions
– Still far away from results
– Focus on common schema definitions
– Toolkits unsure: GML, RDF
the open planning project
Issue: Projections
• Issue
– EPSG is standard
– Limitations to EPSG database
• Approaches
– External WKT
• Conclusions
– Integrated XML encoding required
– Coming in GML3
the open planning project
Future Work: GeoTools2
• GML Parsing
– Handle non-flat features
– GML3
• GML Generation
– Integration happening now
the open planning project
Future Work: GeoServer
• GeoTools2 Integration (1 month)
– Transactional WFS
– Internal Filtering
– Data Support
• Shape, MIF, MySQL, CSV
• SLD/WMS (2 months)
• Other (ongoing)
– GML3
– WCS
– Data Formats
• ArcSDE, Oracle 9i Spatial
the open planning project
Future Work: Virtual Terrain
• Internal representation
– Custom text to GML
– Generic cultural object representations
• Run-time WFS/WCS 3D support
– Current imports in 2D functional
– Fully interactive 3D scene browsing
• Whole Earth Paging
• Browser plug-in
the open planning project
Conclusions
• Historical reluctance to develop tools
– Underlying tech developing (XML, Schema)
– Confusion over standard
• GML Schema requirement
• Some successes
– Hesitation with coming of GML3
• Some tools now available
– Parsers generally bound to toolkit
the open planning project
Conclusions
• More tools will develop
– Underlying technologies stabilizing
– GML3 (hopefully) will solve
• Waiting for the next big thing
• Confusion over standards
• When to use Open Source
– Time to develop not critical
– Cost is critical
– Vendor independence critical
the open planning project
Conclusions
• What to use?
– GML4j, GeoTools2, OGR/GDAL
– Commercial vendors
• URLs
–
–
–
–
–
–
TOPP: http://www.openplans.org
GeoServer: http://geoserver.sourceforge.net
Virtual Terrain: http://vterrain.org
GeoTools: http://www.geotools.org
OGR/GDAL: http://remotesensing.org
PostGIS: http://postgis.refractions.net