# Presentation: 053478

## WCSplus

- Making the Web Coverage Service work for the Fluid Earth Sciences Community

- Bruce Wright (Senior IT Architect), 7th GO-ESSP Community Workshop, 17-19 September 2008

## 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)

## Contents

- This presentation covers the following areas
- OGC Standards
- Web Coverage Service
- WCSplus
- Example Comparison
- The Future
- Discussion

## OGC Standards

- (Open Geospatial Consortium)
- http://www.opengeospatial.org/

## 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

## 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

## WCS

- (Web Coverage Service)
- http://www.opengeospatial.org/standards/wcs

## WCS Request

- HTTP GET with KVP (or POST with either XML or SOAP....or RESTful?):
- URL of service: http://host[:port]/path?
- Standard request parameters: SERVICE=WCS&VERSION=1.0.0
- 3 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

## 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)

## 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 19123 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

## WCSplus

- http://www.unidata.ucar.edu/mailing_lists/archives/wcsplus/
- (Also: http://galeon-wcs.jot.com/WikiHome/GALEON%20Phase2%20Main%20Page)

## 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)

## 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)

## 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 07-112 proposal for ISO 19123 irregular grids)

## WCSplus  – ‘Ingredients’ (2)

- Allow multiple times
- Allow non-spatial vertical coordinate
- Specification fully based on ISO 19123 coverage specification
- Sort inconsistencies in KVP and XML schema documents

## WCSplus – Implementation

- Suggested:
- Be more explicit about HTTP response codes
- Use HTTP GET with KVP only

## Example Comparison

- http://galeon-wcs.jot.com/WikiHome/GALEON%20Phase2%20Main%20Page/GALEON%202%20WCS%20Servers

## 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 | 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 WCS | 
THREDDS WCS (1.0.0) |
| --- | --- |

## The Future

## 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

## Forthcoming Activities 

- September '08 OGC Technical Committee Meeting, Atlanta Georgia, 15-19 Sept 2008
- 	_[http://www.opengeospatial.org/event/0809tc](http://www.opengeospatial.org/event/0809tc)_
- Workshop on the use of GIS/OGC standards in meteorology, ECMWF, Reading, UK, 24-26 Nov 2008
- 	_[http://www.ecmwf.int/newsevents/meetings/workshops/2008/OGC_workshop/index.html](http://www.ecmwf.int/newsevents/meetings/workshops/2008/OGC_workshop/index.html)_
- December '08 OGC Technical Committee Meeting, Valencia, Spain, 1-5 Dec 2008
- 	_[http://www.opengeospatial.org/event/0812tc](http://www.opengeospatial.org/event/0812tc)_

## Questions and answers

- Discussion