© Crown copyright Met Office WCSplus Making the Web Coverage Service work for the Fluid Earth Sciences Community Bruce Wright (Senior IT Architect), 7 th GO-ESSP Community Workshop, September 2008

© Crown copyright Met Office Collaborators Ben Domenico, Ethan Davis, Jon Caron (Unidata) Stefano Nativi, Paolo Mazzetti (University of Florence) Andrew Woolf, Dominic Lowe (Science and Technology Facilities Council, RAL) Jon Blower (Reading e-Science Centre) Jeremy Tandy (Met Office)

© Crown copyright Met Office Contents This presentation covers the following areas OGC Standards Web Coverage Service WCSplus Example Comparison The Future Discussion

© Crown copyright Met Office OGC Standards (Open Geospatial Consortium)

© Crown copyright Met Office Open Geospatial Consortium (OGC) International industry consortium of 366 companies, government agencies and universities Consensus process to develop publicly available interface specifications to support interoperable solutions that "geo-enable" the Web, wireless and location-based services, and mainstream IT Specifications that empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications ‘Partner’ with ISO/TC 211 Geographic information / Geomatics – many OGC standards are ISO191xx standards

© Crown copyright Met Office OGC Standards XML grammar and file format for modelling and storing geographic features XML grammar and file format for modelling and storing geographic features for display – submitted by Google to be evolved within the OGC consensus process HTTP interface for retrieving geographic features across the Web using platform-independent calls – GML is the default payload encoding for transporting the geographic features HTTP interface for retrieving geo-registered map images across the Web using platform-independent calls – a request defines the geographic layer(s) and area of interest to be processed and the payload is usually a map image format (e.g. PNG, JPEG) HTTP interface for retrieving geospatial "coverages" (gridded data) across the web using platform- independent calls – the default payload is one of a number of standard binary file formats Geography Markup Language Keyhole Markup Language Web Feature Service Web Map Service Web Coverage Service GML KML WFS WMS WCS

© Crown copyright Met Office WCS (Web Coverage Service)

© Crown copyright Met Office WCS Request HTTP GET with KVP (or POST with either XML or SOAP….or RESTful?): URL of service: Standard request parameters: SERVICE=WCS&VERSION= types of request (REQUEST=): GetCapabilities – Service metadata (XML doc) DescribeCoverage – Full description of one or more coverage (XML doc) GetCoverage – One coverage (known format) Other standard request parameters

© Crown copyright Met Office WCS 1.0 Only a single coverage can be retrieved (homogeneous range set) 2D only, request & response can be different Can be 2D or 3D Only a single time dimension Number of gridpoints Grid-spacing must be regular Interpolation (5 options) Single data file returned – easy to parse (should support at least one GeoTIFF, HDF-EOS, DTED, NITF, GML) Additional “range set parameters” – extends capability, but leads to different approaches Limited set of other GetCoverage request parameters: COVERAGE CRS BBOX TIME WIDTH / HEIGHT / DEPTH RESX / RESY / RESZ INTERPOLATION FORMAT “PARAMETER” (e.g. ELEVATION)

© Crown copyright Met Office WCS 1.1 More bulky and complex than WCS 1.0 – attempt to satisfy all use cases in one standard Changes to request parameters (e.g. COVERAGE - > IDENTIFIER ) Reduced ISO conformance Still only get one ‘coverage’ – but can support coverage hierarchies, each composed of multiple (non-homogeneous) fields 0,1,2 or 3D – but still regularly spaced Still 1 time dimension Adds far more extensive CRSs (including vertical) – but still not straight forward to handle non-height-based vertical coordinate Scalar or vector fields Any format now acceptable (depreciated ‘blessed 5’), but should have WCS encoding profile GetCoverage response always encoded as ‘Coverage XML doc’, which references 1 or more data files, which are either: Bundled in MIME multi-part message, or: Accessible via separate URL (STORE) – not full asynchronous capability

© Crown copyright Met Office WCSplus (Also:

© Crown copyright Met Office WCSplus – History OGC Technical Committee meeting (Boulder, Sep 2007); Unidata hosted an Interoperability Day Addressing use of standard interfaces (inc. WCS) for providing access to data currently served via THREDDS, OPeNDAP, CF-netCDF, etc for the Fluid Earth Sciences (FES) community Subsequent discussions resulted in the WCSplus (originally WCS 1.0+) initiative WCSplus mailing list established Really a subset of the OGC GALEON (Geo- interface for Air, Land, Environment, Ocean NetCDF) IE (Interoperability Experiment)

© Crown copyright Met Office WCSplus – Philosophy Start with WCS 1.0 Relatively simple Already a substantial number of working implementations Develop practical & concrete ideas to meet FES community requirements Trade-off between generality/powerfulness and simplicity/feasibility -> minimal changes -> relatively easy to implement & test Validate through the implementation and experimentation with specific additional features (GALEON 2) Feed back into the WCS standard via the WCS Standards Group (WCS 1.2)

© Crown copyright Met Office WCSplus – ‘Ingredients’ (1) CF-netCDF binary encoding – Ben Domenico & Stefano Nativi developing a “WCS 1.1 extension for CF-netCDF 3.0 encoding” (Oct 2008) Asynchronous response handling – Discussion paper from Ethan Davis, Stefano Nativi & Paolo Mazzetti (Nov 2007), drawing GADS-WCS Interface Spec from Jon Blower (Mar 2006) Multiple heterogeneous fields within a coverage – change ‘range set’ model & AxisDescription Support for irregular grids - Use GML with CR that includes CV_ReferencableGrid (see OGC proposal for ISO irregular grids)

© Crown copyright Met Office WCSplus – ‘Ingredients’ (2) Allow multiple times Allow non-spatial vertical coordinate Specification fully based on ISO coverage specification Sort inconsistencies in KVP and XML schema documents

© Crown copyright Met Office WCSplus – Implementation Suggested: Be more explicit about HTTP response codes Use HTTP GET with KVP only

© Crown copyright Met Office Example Comparison wcs.jot.com/WikiHome/GALEON%20Phase2%20Main%20Page/GALEON% 202%20WCS%20Servers

© Crown copyright Met Office Visual Weather vs. THREDDS Service Data source (e.g. all Global model runs) Single instance of data source (e.g. a single Global model run) COVERAGE Met parameter (e.g. temperature) but no standard names Spatial domain 2D BBOX + ‘ ELEVATION ’ range parameter 3D BBOX + ‘ VERTICAL ’ range parameter Time domain TIME for validity time + ‘ DIM_RUN ’ & ‘ DIM_FORECAST ’ range parameters for analysis time and forecast period TIME for validity time (Analysis time is covered by service) Ensembles ‘ DIM_ENSEMBLE ’ range parameter (not implemented yet) Not implemented? FORMAT NetCDF3, GeoTIFF, GeoTIFFfloat, GRIB1, KML NetCDF3, GeoTIFF, GeoTIFFfloat VW WCSTHREDDS WCS (1.0.0)

© Crown copyright Met Office The Future

© Crown copyright Met Office WCS 1.2 Different Approach: Rather limited ‘core’ – possibly only 2D Set of extensions WCSplus capability realised through: FES Application Profile Number of relevant programmatic extensions – e.g. extension for CF-netCDF 3.0 encoding + Workable standard for our community – Issues with inter-community interoperability

© Crown copyright Met Office Forthcoming Activities September '08 OGC Technical Committee Meeting, Atlanta Georgia, Sept Workshop on the use of GIS/OGC standards in meteorology, ECMWF, Reading, UK, Nov _workshop/index.html December '08 OGC Technical Committee Meeting, Valencia, Spain, 1-5 Dec

© Crown copyright Met Office Questions and answers Discussion