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

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

3 Disparate Data Models: Different Ways of Thinking about Data To the GIS (solid earth and societal impacts) community, the world is: features –A collection of static features (e.g., roads, lakes, plots of land) with geographic footprints on the Earth (surface). features discrete objects database. –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: parameters continuous functions –A set of parameters (e.g., pressure, temperature, wind speed) which vary as continuous functions in 3-dimensional space and time. parameters equations. –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.

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

5 Typical NetCDF Visualization

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

7 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)

8 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

9 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

10 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?

11 Primary OGC Interface Issues NetCDF as a sixth WCS encoding format OR Develop netCDF application profile ANDDevelop netCDF application profile AND Do away with fixed list of encoding formats (geoTIFF, HDF-EOS, NITF, DTED, GML)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?)

12 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

13 netCDF – Coverage Mapping (S. Nativi) Explicit mediation needed between netCDF hyperspatial data and WCS coverage models netCDF datasetWCS coverage N independent dimensions (i.e. axes)2, 3, 4 coverage domain dimensions Set of scalar variablesCoverage range-set of values (t, z, y, x) variable shape(x, y, z, t) domain shape Implicit geo-location metadataExplicit geo-location metadata Grid geometry irregularly spacedGrid geometry regularly spaced etc.

14 NetCDF-CF dataset content (S. Nativi)

15 WCS coverage content (S. Nativi)

16 2 Dimension Coordinate System Implicit/explicit Geometry Range set Spatial Reference System (SRS) 2 Dimension Coordinate System Implicit/explicit Geometry Range set Spatial Reference System (SRS) 2 Dimension Coordinate System Implicit/explicit Geometry Range set Spatial Reference System (SRS) 2 Dimension Coordinate System Implicit/explicit Geometry Range set Spatial Reference System (SRS) Mediation Process (S. Nativi) netCDF hyperspace dataset (3/4/5D) 2D + elev + time Coverages 2D+elev+time dataset 2D SCS + elev + time Implicit/explicit Geometry Range set Spatial Reference System (SRS) a Coverage … … N-Dimension Coordinate Systems explicit/semi-implicit/implicit Geometry Scalar measured quantities

17 Basic mapping concepts (S. Nativi) A netCDF dataset contains several different coverages Each coverage is characterized by a domain, a range- set and is referenced by a CS/CRS Each coverage is optionally described by a geographic extent Each domain is characterized by a geometry –Supported domains: regular grid domain, irregular grid domain and multipoint domain Each range-set lists or points set of values associated to each domain location –Supported range-set types: scalar range-set and parametric range-set

18 netCDF-related Changes 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?

19 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

20 References GALEON Wiki Wiki OGC portal GALEON area portal GALEON area Phase 2 implementation plan hase2_Implementations.htmPhase 2 implementation plan hase2_Implementations.htm OGCnetwork Draft CF-netCDF WCS Encoding Profile short.htmDraft CF-netCDF WCS Encoding Profile short.htm