Web Coverage Service

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The Open Geospatial Consortium Web Coverage Service interface standard ( WCS ) defines the web- based query of digital geospatial information that depicts phenomena that vary in space and / or time.

overview

WCS provides access to coverage data in forms that can be used for client-side processing, such as scientific models. The WCS is related to the OGC Web Feature Service (WFS) and Web Map Service (WMS). As a service instance of the WMS and the WFS, a WCS allows clients to select parts of the information inventory of a server based on spatial conditions and other query criteria.

In contrast to the Web Map Service (WMS), which delivers geographic data as map images, the WCS provides available data together with their detailed descriptions (metadata) and defines a rich syntax for queries on this data and metadata. In particular, data is returned with its full semantics when it is delivered; In contrast to the WMS images, which are only suitable for humans, WCS data can therefore also be further evaluated automatically.

In contrast to the Web Feature Service (WFS), which supplies individual spatial data elements, WCS returns multidimensional data that brings a section of the space-time properties into any relationship. As such, WCS focuses on coverages as a specialized class of features (namely sets of features) and offers corresponding functionality.

WCS is based on the coverage model of the OGC GML Application Schema for Coverages and supports all coverage types from it. In particular, the current version 2.0 is no longer restricted to regular grids like earlier WCS versions.

WCS Core, extensions and application profiles

WCS Suite: Logical View

The WCS Suite is subdivided into a core that every WCS implementation must support, plus a number of extensions with additional service facets. During the implementation, you can choose which extension should be supported. Only a few basic rules have to be met: Every WCS implementation must support at least one communication protocol and one data output format. To make the overview easier, the extensions are grouped into five categories: data model, coding, service model, protocols and usability.

To make it easier for the implementers to choose extensions, application profiles were established as domain-oriented "bundles" of the WCS suite. They serve as guidelines for the implementation of WCS services for specific areas of application.

Selected specifications are briefly presented below.

The documents of the WCS standard are available on the OGC-WCS page.

WCS Core

WCS trim and slice

The WCS Core provides basic spatial and temporal data extraction. There are two types of extraction that can be combined: Trimming extracts a section of a coverage, defined by a bounding box ; the result has the same dimension (i.e. the number of axes) as the original coverage. Slicing makes a cut at the specified position, thereby reducing the dimension of the result coverage.

From a technical point of view, the WCS core offers three request types, according to the OGC web service definition:

  • GetCapabilities : supplies an XML description of the service properties and data sets offered by the requested server,
  • DescribeCoverage : supplies XML descriptions of the coverages (e.g. their position in space and time),
  • GetCoverage : delivers a coverage (or part of it), either as original data or converted into a suitable data format.

WCS protocol extensions

WCS requests and responses can use the following protocols:

  • GET / KVP: uses HTTP GET to send requests in the form of key-value pairs (KVP) and receives XML metadata and binary coverage data.
  • POST / XML: uses HTTP POST for the transfer of XML data and binary coverage data.
  • SOAP / XML: uses SOAP for the transmission of XML data and binary coverage data.
  • REST : This protocol variant is currently under development.

WCS extensions for data formats

WCS extensions for formats allow coverage to be returned in different data formats such as B. GML , GeoTIFF , HDF-EOS or NITF . A number of these specifications are currently (as of June 2013) available as candidate standards.

WCS range subsetting

Range subsetting (not to be confused with the domain subsetting of the WCS Core) allows the extraction of components (“bands”, “channels”) from cells (“pixels”, “voxels”) of a coverage.

For example, a range subsetting request can extract the near-infrared, red and green components from a 7-band Landsat satellite image. The spatial scope remains unchanged.

WCS-T extension

WCS-T (T stands for transaction) defines how new coverages can be uploaded to a server and how existing coverages can be changed.

WCS processing extension

Web Coverage Processing Service (WCPS) defines flexible ad hoc processing and filtering on coverage quantities. The Processing Extension integrates the abstract WCPS query language into the protocols of the WCS suite.

WCS CRS extension

The WCS CRS (Coordinate Reference System) extension allows coverages to be addressed in coordinate reference systems that differ from the original coordinate system in which the coverages are stored on the server. This extension therefore allows a CRS transformation or reprojection.

Software support for WCS

OGC Compliance Testing

OGC provides the free, open source Compliance and Interoperability Test Engine (CITE), so that a given implementation can be tested for compliance with a given OGC specification. A list of all specification tests available from the OGC can be found on the OGC compliance page.

WCS implementations

A list of implementations for which the OGC standard conformity has been officially confirmed is published on the OGC website. See also the discussion “compliant vs implementing”.

This is an unofficial, unchecked and not confirmed by OGC list of implementations that support WCS as a client or server:

  • WCS 2.0:
    • Rasdaman - server and client (read / write); Reference implementation for WCS 2.0, reference implementation for WCPS
    • MapServer server
    • PYXIS WorldView - Free client, integrates various data sources on a hexagonal discrete global grid

Individual evidence

  1. ↑ OGC 09-146r1 opengeospatial.org
  2. ↑ OGC Web Coverage Service standard document download
  3. ↑ external.opengeospatial.org
  4. ↑ Compliance and Interoperability Test Engine (CITE)
  5. ^ OGC Compliance Testing
  6. ↑ OGC list of compliant products . opengeospatial.org
  7. ↑ compliant vs implementing. OGC FAQ
  8. ↑ rasdaman - Big Array Data Analytics Server, including Web client toolkit (raswct)
  9. ↑ OGC Network: Web Coverage Service ( Memento of the original from December 17, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.ogcnetwork.net
  10. ↑ MapServer WCS Server . Retrieved October 23, 2013.
  11. ↑ a b PYXIS WorldView GeoWeb Browser . Retrieved October 23, 2013.
  12. ↑ ERDAS APOLLO . Archived from the original on April 6, 2011. Retrieved October 23, 2013.
  13. ^ GDAL Web Coverage Service . Retrieved October 23, 2013.
  14. ↑ PCI Geomatics' Web Coverage Server successfully passes compliancy testing . Archived from the original on October 22, 2012. Retrieved October 23, 2013.
  15. ↑ ESRI ArcGIS Server . Retrieved October 23, 2013.
  16. ^ CARIS Spatial Fusion Enterprise . Retrieved October 23, 2013.