OGC Spatio-Temporal Coverage / Datacube Standards
Table of Contents:
- "Web developers who have not heard of OGC standards before immediately feel at home with these coverage standards" -- Stephan Siemen, ECMWF
- "WCS is the natural way to deliver and exploit coverage data." -- Jordi Escriu, Facilitator INSPIRE Thematic Cluster #3: Elevation, Orthoimagery, Reference systems and Geographical grids
- "As a WCS the data is of most value" -- Perry Peterson, Pyxis Innovation
- "CIS 1.1 is what I've been waiting for." -- Kathi Schleidt, INSPIRE expert
- "CIS 1.1 addressed many of the issues faced with CIS 1.0 and GML 3.3 coverages in a neat way." -- Ilkka Rinne, INSPIRE expert
- "The WCS 2.0 XML schema set is much easier to use than the 1.x XML; it validates and is better organized" -- OPeNDAP
Note: you can reach this site under the shortcut http://myogc.org/go/coveragesDWG .
Maintainer of this wiki is Peter Baumann
and rasdaman GmbH
), further contributors are welcome.
s - as per OGC, ISO, and INSPIRE standardization - constitute a unifying paradigm for the digital representations of space/time varying phenomena, concretely: spatio-temporal regular and irregular grids, point clouds, and general meshes. In particular, multi-dimensional datacubes
fall under this category, such as 1-D sensor time series, 2-D satellite imagery, 3-D x/y/t image time series and x/y/z geoscientific models, 4-D x/y/z/t climate and ocean data sets, and more.
This data model is accompanied by a modular service model, the Web Coverage Service
(WCS) suite of standards. Functionality of this Web API ranges from flexible datacube access and subsetting up to complex geo datacube analytics with the Web Coverage Processing Service
(WCPS) datacube language.
While still fomat-independent, this conceptual overage model is conformance testable down to pixel level and harmonized with GML, SWE, and other OGC standards, thereby concretizing the abstract and therefore not interoperable ISO 19123 model.
This site is part of the Open Geospatial Consortium
(OGC) and maintained by its Coverages Domain Working Group
(Coverages.DWG) which uses this site for providing information about standardization of coverages.The OGC Coverages.DWG is a community oriented working group established for facilitating exchange on the OGC coverage data and service standards
. The Coverages.DWG does not directly revise OGC standards
, but rather enables collaboration and communication between groups with spatio-temporal modeling interests. See also the Temporal.DWG
which specifically addresses temporal data aspects.
The group is chaired by Peter Baumann ( Jacobs University Bremen
and rasdaman GmbH
) and Stephan Meissl ( EOX IT Services GmbH
This Twiki as well as the corresponding email list
provide information about the standards, including tutorials and the authoritative specification sources. Further, it constitutes a public forum for communication. Anyone can edit this wiki, but, of course, responsibly. Instructions can be found on the TWiki Text Formatting Rules
There is a large amount of introduction and training material available, listed from overview to detailed:
- ISO TC211:
- ISO 19123-1: Abstract coverage model; currently being reworked from ISO 19123 = OGC Abstract Topic 6; after ISO adoption it is planned to update OGC AT6 to stay in sync.
- ISO 19123-2: Coverage Implementation Schema = CIS 1.0; next step: extend with CIS 1.1 GeneralGridCoverage
- INSPIRE (legal framework for a common European SDI):
- June 2020: ISO TC211 WG6 has distributed a Working Draft of 19123-1, the forthcoming abstract coverage standard complementing the concrete 19123-2 = OGC CIS.
- 2019: WCS 2.1 have been adopted, together with updates in the corresponding WCS extensions. This adds GeneralGridCoverage as a unified, simplified coverage type encompassing all raster / gridded coverage types.
- July 2019: ISO adopts SQL/MDA (Multi-Dimensional Arrays) as 9075-15:2019. Thi Part 15 of SQL adds datacube analytics into the database language. Note that OGC WCPS is structurally equivalent to SQL/MDA (WCPS requests can be transformed automatically into SQL), however WCPS adds spatial and temporal semantics whereas MDA is domain-agnostic and can handle Earth, Space, and Life science data.
- September 2017: At the Southampton TC meeting the Coverages.DWG has moved to approve establishing a Datacube Domain Working Group; close collaboration between the Coverages.DWG and the forthcoming Datacube.DWG is planned as the OGC datacube standard is the Coverage Implementation Schema.
- April 2017: CIS 1.1 is adopted by OGC as an Interface Standard. This opens the way for introducing CIS 1.1 to ISO to become the next version of ISO 19123-2.
WCS enjoys a large and growing number of implementations, such as the following:
- OGC compliance listing (search for "wcs")
- open-source projects: rasdaman (WCS Core Reference Implementation), MapServer, EOxServer, GeoServer, GDAL, QGIS, OpenLayers, OPeNDAP/Hyrax, George Mason University, NASA GSFC, openEO, ...
- commercial products: Envitia ChartLink, Pyxis WorldView Studio, Constellation-sdi, Pixia, ESRI ArcGIS, ...
Note that the list above is not authoritative (the page maintainers do not regularly check the links) and does not constitute any endorsement nor a statement of OGC nor anybody else about conformance. Information is provided as is, without any warranty.
The current version of WCS is 2.1. Functionally, it is identical to its predecessor WCS 2.0.1, but it extends the coverage types serviceable with GeneralGridCoverage as per CIS 1.1. This new coverage type unifies and simplifies grid coverages, in particular incporporating RectifiedGridCoverage and ReferenceableGridCoverage as pwe WCS 2.0.
WCS 2.0 has several significant advantages over previous versions: it relies on the GML coverage model, leading to increased interoperability as well as harmonization across OGC standards; among the main features are:
- extends beyond pure raster grids to support all coverage types which GML 3.2.1 knows, e.g., curvilinear grids, irregular grids, point clouds, surface coverages; general meshes;
- crisp and modular, consisting of a small mandatory core and a structured universe of optional extensions;
- harmonized with OGC OWS-Common, GML, SWE, WMS, WCPS, and WPS
- has a clear, formally specified syntax (XML Schema) and semantics (Schematron) easing understanding and implementation;
- testable: for the first time, pixel contents is subject to conformance testing. In other words: conformance of coverage data and services can be tested down to single pixel level.
WCS 1 is the outdated, deprecated version of WCS. It is not compatible with WCS 2, as indicated by the major version number change (cf. OGC versioning rules). WCS 1, a stepstone in the learning curve about coverages, suffered from some known issues, in particular: lack of interoperability. It had its own coverage model which has been abondoned in WCS 2 for the sake of aligning with GML coverages.