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?

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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

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Product: GeoServer

– J2EE – Full non transactional WFS – Reads from PostGIS – Full transactional support

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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

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Open Source GML Libraries

• Java – GML4J (Galdos) – GeoTools (Leeds/TOPP) – OpenMap (BBN) – Geobject? (Polexis) • C++ – OGR (Warnerdam) • Other Languages – ?

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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

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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

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Open Source Generators

• GeoServer – Known to have interoperated • Academic – UMN MapServ (planned) – Other academic projects • Nothing packaged • Commercial – Under a dozen

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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

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Open Issues

• Base Issue – Dealing with the complexity of GML features • Overview – Feature Type Complexity – Internal Feature Types – Schema Proliferation – Projections

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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

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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

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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

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Issue: Projections

• Issue – EPSG is standard – Limitations to EPSG database • Approaches – External WKT • Conclusions – Integrated XML encoding required – Coming in GML3

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Future Work: GeoTools2

• GML Parsing – Handle non-flat features – GML3 • GML Generation – Integration happening now

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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

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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

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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

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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

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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