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 1

Outline

• Two communities: Background • Phase 1 Accomplishments, • Phase 2 Directions • WCS Implications • Observations

(Many slides just for future reference) 2

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 time.

parameters

(e.g., pressure, temperature, wind speed) which vary as continuous functions in 3-dimensional space and – The behavior of the

parameters

in space and time is governed by a set of – Data are simply discrete points in the mathematical function space.

equations.

3

Attributes in DBMS tables

Traditional GIS view

Features as points, lines, polygons

4

Typical NetCDF Visualization

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Taking Advantage of Web Services for Data System Interoperability

GIS Client Applications OGC or proprietary GIS protocols

OpenGIS Protocols: WMS, WFS, WCS

FES Client Applications OGC or OPeNDAP ADDE. FTP… protocols GIS Servers GIS Server GIS Server societal impacts, … datasets FES Servers THREDDS Server THREDDS Server forecast model output, … datasets

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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

Protocol) (Open Project for Networked Data Access –

THREDDS

(THematic Real-time Environmental Distributed Data Services) 7

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 8

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 9

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? 10

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?) 11

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 N independent dimensions (i.e. axes) Set of scalar variables (t, z, y, x) variable shape Implicit geo-location metadata Grid geometry irregularly spaced etc.

WCS coverage 2, 3, 4 coverage domain dimensions Coverage range-set of values (x, y, z, t) domain shape Explicit geo-location metadata Grid geometry regularly spaced etc.

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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?

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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 19

References

• GALEON Wiki http://galeon-wcs.jot.com/WikiHome • OGC portal GALEON area http://portal.opengeospatial.org/index.php?m=projects&a=view&project_id=173 • • Phase 2 implementation plan http://www.unidata.ucar.edu/projects/THREDDS/GALEON/GALEON2_P hase2_Implementations.htm

OGCnetwork http://www.ogcnetwork.net/?q=networks • Draft CF-netCDF WCS Encoding Profile http://www.unidata.ucar.edu/projects/THREDDS/GALEON/netCDFprofile short.htm

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