Ben Domenico Unidata Program Center*

International Standards for Data InteroperabilityGALEONGeo-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

Outline • Two communities: Background • Phase 1 Accomplishments, • Phase 2 Directions • WCS Implications • Observations (Many slides just for future reference)

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 features (e.g., roads, lakes, plots of land) with geographic footprints on the Earth (surface). • The features are discrete objects with attributes which can be stored and manipulated conveniently in a database. • To the fluids (atmosphere and oceans) communities, the world is: • A set of parameters (e.g., pressure, temperature, wind speed) which vary as continuous functions in 3-dimensional space and time. • The behavior of the parameters in space and time is governed by a set of equations. • Data are simply discrete points in the mathematical function space.

Traditional GIS view Features as points, lines, polygons Attributes in DBMS tables

Typical NetCDF Visualization

FES Client Applications GIS Client Applications FES Servers GIS Servers THREDDS Server GIS Server THREDDS Server OGC or OPeNDAPADDE. FTP… protocols OpenGIS Protocols: WMS, WFS, WCS Satellite, radar, forecast model output, … datasets OGC or proprietary GISprotocols GIS Server Demographic, infrastructure, societal impacts, … datasets Taking Advantage of Web Services for Data System Interoperability

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)

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

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

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?

Primary OGC Interface Issues • NetCDF as a sixth WCS encoding format OR • Develop netCDF application profile AND • Do away with fixed list of encoding formats (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?)

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

netCDF – Coverage Mapping (S. Nativi) Explicit mediation needed between netCDF hyperspatial data and WCS coverage models

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?

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

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

Ben Domenico Unidata Program Center*