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International Standards for Data Interoperability

GALEON Geo-interface for Air, Environment, Land,

Ocean NetCDF

Ben DomenicoUnidata Program Center*

For KNMI Atmospheric Data Access for the Geospatial User Community

September 2006

*Sponsored by U. S. National Science Foundation

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Outline

• Two communities: Background

• Phase 1 Accomplishments,

• Phase 2 Directions

• WCS Implications

• Observations(Many slides just for future reference)

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Disparate Data Models:Different Ways of Thinking about Data

• To the GIS (solid earth and societal impacts) community, the world is:– A collection of static featuresfeatures (e.g., roads, lakes, plots of land)

with geographic footprints on the Earth (surface).– The featuresfeatures are discrete objectsdiscrete objects with attributes which can be

stored and manipulated conveniently in a database.database.

• To the fluids (atmosphere and oceans) communities, the world is:– A set of parametersparameters (e.g., pressure, temperature, wind speed)

which vary as continuous functionscontinuous functions in 3-dimensional space and time.

– The behavior of the parametersparameters in space and time is governed by a set of equations.equations.

– Data are simply discrete points in the mathematical function space.

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Traditional GIS view

Attributes in DBMS

tables

Features as points,

lines, polygons

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Typical NetCDF Visualization

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Taking Advantage of Web Services for Data System Interoperability

GIS ClientGIS Client Applications Applications

FES ClientFES Client Applications Applications

OpenGIS Protocols:WMS, WFS, WCS

OGC or proprietary GIS

protocols

OGC or OPeNDAPADDE. FTP…

protocols

GIS ServerGIS Server

GIS ServersGIS ServersDemographic, infrastructure, Demographic, infrastructure,

societal impacts, … societal impacts, … datasetsdatasets

THREDDS ServerTHREDDS ServerFES ServersFES Servers

Satellite, radar, Satellite, radar, forecast model output, … forecast model output, …

datasetsdatasets

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GALEON Objectives• Use standardized web service between GIS and

atmospheric/oceanographic clients and servers• Determine suitability of WCS (Web Coverage

Service) interface for serving traditional ES datasets to GIS community

• Implement WCS gateway(s) to existing FES client/server community, based on:– *netCDF (network Common Data Form),– OPeNDAP (Open Project for Networked Data Access

Protocol)– THREDDS (THematic Real-time Environmental

Distributed Data Services)

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Accomplishments• Interoperability experiments with WCS

client and server implementations at numerous sites (status reports on GALEON wiki and OGC portal)

• Several recommendations for changes to WCS specification (formal documents on OGC portal)

• Initiatives underway for GML applications profiles for explicit netCDF semantics (ncML-GML, CSML)

• Dialog initiated with GMLJP2 group to determine applicability to netCDF datasets

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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

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Phase 2 Questions• Is WCS 1.1 adequate for serving netCDF

datasets such as those on the servers at Unidata, the University of Florence, George Mason University, NERC, NCDC, and the PFEL?

• Is the CSW interface adequate for cataloging the collections of data in question 1 above and how do clients interact with both WCS and CSW?

• What are the roles of GML dialects (ncML-GML, CSML, GMLJP2) in the context of the GALEON WCS experiments?

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Primary OGC Interface Issues• NetCDF as a sixth WCS encoding format OR• Develop netCDF application profile Develop netCDF application profile ANDAND

• Do away with fixed list of encoding formats Do away with fixed list of encoding formats (geoTIFF, HDF-EOS, NITF, DTED, GML)(geoTIFF, HDF-EOS, NITF, DTED, GML)

• Develop WCS application profile for netCDF• Augment WCS specification• Develop GML application schemas for

netCDF semantics (ncML-GML, CSML, GMLJP2?)

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CF-netCDF WCS 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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netCDF – Coverage Mapping (S. Nativi)

Explicit mediation needed between netCDF hyperspatial data and

WCS coverage models

netCDF dataset WCS coverage

N independent dimensions (i.e. axes) 2, 3, 4 coverage domain dimensions

Set of scalar variables Coverage range-set of values

(t, z, y, x) variable shape (x, y, z, t) domain shape

Implicit geo-location metadata Explicit geo-location metadata

Grid geometry irregularly spaced Grid geometry regularly spaced

etc. etc.

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netCDF-relatedChanges Proposed in WCS 1.1

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

• Replace binary encoding format list with set of Multiple “variables” or “parameters” 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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Observations and Assessment• A handful of clients and servers have demonstrated

feasibility• Commercial vendors are actively participating (RSI,

ESRI, others)• 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• WCS should be viable (but evolving slowly) within a

year

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References• GALEON Wikihttp://galeon-wcs.jot.com/WikiHome

• OGC portal GALEON areahttp://portal.opengeospatial.org/index.php?m=projects&a=view&project_id=173

• Phase 2 implementation planhttp://www.unidata.ucar.edu/projects/THREDDS/GALEON/GALEON2_Phase2_Implementations.htm

• OGCnetworkhttp://www.ogcnetwork.net/?q=networks

• Draft CF-netCDF WCS Encoding Profilehttp://www.unidata.ucar.edu/projects/THREDDS/GALEON/netCDFprofile-short.htm