Web Coverage Service

The Open Geospatial Consortium Web Coverage Service Interface Standard ( WCS ) defines the web-based retrieval of digital geospatial information representing space and / or time-varying phenomena.

  • 3.1 OGC Compliance Testing
  • 3.2 WCS implementations

Overview

WCS provides access to coverage data in forms that are useful for client - side processing, for example for scientific models. The WCS is related to OGC Web Feature Service (WFS ) and Web Map Service ( WMS). As a service instance of the WMS and WFS allows the WCS clients to choose portions of a server's information holdings based on spatial conditions and other search criteria.

In contrast to the WMS, which provides geo- data as map images, the WCS available data together with their detailed descriptions (metadata) and defines a rich syntax for requests on these data and metadata. In particular, data are delivered returned with their full semantics; in contrast to the suitable only for people images of the WMS to WCS data can therefore evaluate machine on.

In contrast to the WFS that provides individual spatial data elements, WCS returns multi-dimensional rDaten that brings a section of the space-time properties in any relationship. As such, WCS focuses on coverage as a specialized class of features (ie, quantities of features ) and provides corresponding functionality.

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

WCS Core, extensions and application profiles

The WCS suite is divided into a core ( " Core" ), the need to support any WCS implementation, plus a number of extensions ( "Extensions" ) with additional services facets. The implementation can be chosen which extension should be supported. Only some basic rules must be met: Each WCS implementation must support at least one communication protocol and a data output format. To facilitate the overview, the extensions are grouped into five categories: data model, encodings, service model, protocols and usability.

To facilitate the implementers the choice of extensions, application profiles ( " Application Profiles " ) as a domain- oriented " bundle " of WCS suite were established. They serve as a guide in the implementation of WCS services for specific application areas.

Selected specifications are presented briefly below.

The documents of the WCS standards are available on the OGC WCS page.

WCS Core

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

From a technical perspective, the WCS core provides three types of requests, according to the OGC Web Service Definition:

  • GetCapabilities: returns an XML description of service properties and data resources that are available from the requested server
  • DescribeCoverage: returns XML descriptions of the coverages (eg, its position in space and time),
  • GetCoverage: provides coverage (or part thereof), 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: use HTTP GET for sending requests in the form of key - value pairs (key value pair, CIP) and receives XML metadata and binary coverage data.
  • POST / XML: using HTTP POST for the transmission of XML data and binary coverage data.
  • SOAP / XML: SOAP used for the transmission of XML data, and binary data coverage.
  • REST: This protocol version is currently in development.

WCS extensions for data formats

WCS extensions for formats allow the return of coverages in different data formats such as GML, GeoTIFF, HDF - EOS or NITF. Currently (as of June 2013) is a series of these specifications before a Candidate Standard.

WCS Range Subsetting

Range subsetting ( not to be confused with the domain subsetting of the WCS Core) allows the extraction of components ( " ribbons ", " channels ) from cells ( " px "," voxel " ) of a coverage.

For example, extracting the near-infrared, red and green components of a 7- band Landsat satellite image a range subsetting request. The spatial extent remains unchanged.

WCS- T extension

WCS -T ( T stands for transaction) defines how new coverages can be uploaded to a server or existing coverages are subject to change.

WCS Processing Extension

Web Coverage Processing Service ( WCPS ) defines flexible ad - hoc processing and filtering on coverage amounts. The processing extension binds the abstract WCPS query language in the protocols of WCS suite.

WCS CRS extension

The WCS CRS ( Coordinate Reference System) extension allows coverages to address in coordinate reference systems that be different from the original coordinate system in which the coverages are stored on the server. Thus, this extension allows a CRS transformation and reprojection.

Software support for WCS

OGC Compliance Testing

OGC is the free, open source compliance and interoperability testing engine ( CITE ) ready, so that for a given implementation, the match can be tested with a given OGC specification. A list of all specification tests that are available from the OGC is to be found on the OGC Compliance page.

WCS implementations

A list of implementations, which the OGC standard - conformity has been confirmed officially, is on the OGC website. published. See also the discussion "compliant vs. Implementing ".

This is an unofficial, not tested and not confirmed by OGC list of implementations that support the 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 different data sources on a hexagonal discrete global grid
  • WCS 1.x: GeoServer - Reference Implementation for WCS 1.x (server)
  • APOLLO - server and client
  • GDAL - client ( read)
  • Geomatica Web Server Suite - Client and server
  • GeoMedia - client (read ) and server ( GeoMedia WebMap )
  • GvSIG - client ( read)
  • ArcGIS Server - Server and Client
  • PYXIS WorldView - Free client integrates different data sources on a hexagonal discrete global grid
  • CARIS Spatial Fusion Enterprise - Server and Client
  • Unidata TDS ( Thredd OPeNDAP data server) - Server
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