1 International Standards for Data Interoperability GALEON Geo-interface for Air, Environment, Land,...
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1 International Standards for Data Interoperability GALEON Geo-interface for Air, Environment, Land, Ocean NetCDF Ben Domenico Unidata 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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Transcript of 1 International Standards for Data Interoperability GALEON Geo-interface for Air, Environment, Land,...
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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
stefano
In the realm of geolocated datasets, data stored in Geographic Information Systems (GIS) are highly structured and most often stored in an underlying relational database. While this may be a gross simplification, GIS datasets typically consist of “features” on the surface of the Earth that can be represented by points, lines and polygons. An example is a county plat which can show natural features such as streams and rivers, infrastructure like roads and bridges and buildings, and plots of land such as towns, lots, and so forth. The attributes of these features lend themselves to storage in the tables of a relational database. There can be a table for the roads, another for the towns, yet another for the rivers, etc. Each specific feature is a record in a table which provides a very useful way of keeping track of the characteristics of each instance of each feature.Visualization is conceptualized in terms of a set of “layers.” In the physical world, transparent mylar sheets are often used to overlay various sets of features on a given base map. The same idea is used for manipulating the visualization of the classes of features in GIS visualization systems
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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
