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Key Results from GALEON

John Caron

Ben DominicoUCAR/Unidata

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Background

• Open GIS Consortium (OGC)– Industry/government consortium for creating

interoperable standards for GIS– Commercial, not open source

• Web Coverage Service (WCS)– Client-server protocol for “coverage” data (satellite

data seems to be their main use case)– XML over HTTP / SOAP– Specification version 1.0 (1.1 almost ready)

• GALEON: OGC “interoperability experiment” for WCS clients and servers

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GALEON Objectives

1. Determine suitability of WCS interface for serving model data to GIS community (4D vs 2D)

2. Examine possibility of extending WCS to add netCDF to current blessed encodings:

– GeoTIFF (TIFF with geospatial tags)– HDF-EOS (HDF4 plus NASA metadata)– DTED (NIMA/DOD digital elevation)– NITF (NIMA/DOD images)– GML (OGC XML data encoding)

3. Experiment with GML (Geography Markup Language) dialects and netCDF files

4. Make recommendations to WCS 1.1 spec

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Active Participants• Unidata/UCAR (Ben Domenico, John Caron) • U of Florence and IMAA-CNR (Stefano Nativi, Lorenzo Bigagli) • International University Bremen (Peter Baumann)• George Mason University (Liping DI, Wenli Yang) • CadCorp (Martin Daly, Frank Warmerdam (GDAL))• Research Systems International UK Ltd (David Burridge, Norman

Barker) (IDL)• NCDC, National Climatic Data Center (Glenn Rutledge, Dan Swank) • NERC Natural Environment Research Council/

British Atmospheric Data Center (Dominic Lowe, Andrew Woolf)• Washington University St. Louis (Stefan Falke, Rudolf B. Husar) • Providing Specialized Expertise

– Interactive Instruments (Clemens Portele)– NASA Geospatial Interoperability Office (John Evans)

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TDS GALEON Development

1. Process WCS GET requests (not SOAP)2. Generate WCS XML documents3. Map bounding boxes to index ranges4. No regridding, no reprojection, want “raw” data5. Create GeoTIFF images

– Greyscale: min/max -> 1..255– DataSample: Floating point (optional for readers)– No standards for missing data, time/vertical– Only implemented a few projections

6. Create subsetted netCDF/CF files7. OPeNDAP WCS service

http://motherlode.ucar.edu:8080/thredds/wcs?dataset=dodsURL

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NERC DataGrid Development

• Created prototype WCS server (with TPAC)• Reads from various “backend providers”

– Currently OPeNDAP– DataExtractor tool (NDG), GADS (Univ Reading),

CSML (NDG)

• Serves subsetted NetCDF/CF• Recommendations to clarify WCS• Investigate CSML as potential format,

referencing netCDF through xlink or gml:File.

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Other WCS/netCDF Servers

• Univ Florence (Nativi et al)– Also experiment with NcML-GML

• Intl Univ Bremen (Baumann et al)– Import netCDF data into PostgreSQL database– Aggregate multiple files into a single database object– Rasdaman maps raster data to relational tuples, SQL

variant queries.• Wash Univ St Louis (Husar et al)

– Also tried to serve collection of irregularly located points

• George Mason University (Liping DI et al)

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WCS/NetCDF clients

• DataFed (Wash Univ St Louis)

• George Mason University

• SIS/GDAL, CadCorp (Martin Daly, Frank Warmerdam (GDAL))

• IDL, Research Systems International

• Non-WCS: – ESRI (local NetCDF/CF files) ArcGIS 9.2

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Accomplishments

• Recommendation for NetCDF as a WCS encoding (1.0)

• Recommendations for changes to WCS 1.1 specification – Peter Baumann – Andrew Wolfe– Stefano Nativi

• Develop netCDF “application profile” (1.1)• Investigation of GML applications profiles for

explicit netCDF semantics (ncML-GML, CSML)

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Plans for Phase 2

• For continued experimentation with WCS implementation, use GALEON OGCnetwork– Additional client & implementations– New datasets

• For WCS and GML specifications, continue as OGC GALEON Interoperability Experiment

• Collaborate closely with:– OGC GEOSS Services Network (GSN)– GMLJP2 (GML JPEG2000)

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CF-netCDF WCS 1.1 Profile• Brief Description • Documentation

– Standard names– Units– Coordinate types– Coordinate systems– Grid mappings– Time coordinate(s)

• Code for Implementing netCDF Interface • Support• CF-netCDF and Coverage (ISO 19123) Data

Model Mapping• Limitations• Compliance Testing

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Changes Proposed in WCS 1.1

• WCS encoding “profiles” instead of fixed list of encoding formats

• Multiple “variables” or “parameters” or “fields” in a coverage (e.g., pressure, temperature, etc.)

• Coverages with 3 spatial dimensions• Coverages with multiple time dimensions (e.g.

forecast time in model output)• Non-spatial “height” dimension, (e.g., atmospheric

pressure, ocean density)• Irregularly-spaced grids• Are collections of point observations and

trajectories coverages or features?

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Summary

• A handful of clients and servers have demonstrated feasibility

• Commercial vendors are actively participating (RSI, ESRI, CADCORP)

• GEOSS demonstrations involve WMS clients getting data from GALEON WCS servers

• Finished netCDF profile is key; other profiles are needed (e.g., OPeNDAP, HDF-EOS, GeoTIFF)

• Most WCS limitations are being addressed in 1.1• With proposed changes, WCS should be viable

for model datasets