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3.4. Web Coverage Service (WCS)

The 1.0.0 and 1.1.1 WCS standards implemented in QGIS Server provide a HTTP interface to access raster data, referred to as coverage, coming from a QGIS project.

Spécifications :

Requêtes standard fournies par QGIS Server:

Requête	Description
GetCapabilities	Renvoie des métadonnées XML avec des informations sur le serveur
DescribeCoverage	Retrieves XML document about additional information about coverages
GetCoverage	Retrieves coverage

3.4.1. GetCapabilities

Standard parameters for the GetCapabilities request according to the OGC WCS 1.1.1 specifications:

Paramètre	Requis	Description
SERVICE	Oui	Name of the service (WCS)
REQUEST	Oui	Nom de la requête (GetCapabilities)
VERSION	Non	Version du service

Outre les paramètres standard, QGIS prend en charge les paramètres suivants :

Paramètre	Requis	Description
MAP	Oui	Fichier du projet QGIS

Exemple d’URL :

http://localhost/qgisserver?
SERVICE=WCS
&VERSION=1.1.1
&REQUEST=GetCapabilities

XML document example when a single raster layer (named T20QPD_20171123T144719_TCI) is published in the QGIS project for the WCS service:

<WCS_Capabilities xmlns="http://www.opengis.net/wcs" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:gml="http://www.opengis.net/gml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0.0" updateSequence="0" xsi:schemaLocation="http://www.opengis.net/wcs http://schemas.opengis.net/wcs/1.0.0/wcsCapabilities.xsd">
  <Service>
    ...
  </Service>
  <Capability>
    ...
  </Capability>
  <ContentMetadata>
    <CoverageOfferingBrief>
      <name>T20QPD_20171123T144719_TCI</name>
      <label>T20QPD_20171123T144719_TCI</label>
      <lonLatEnvelope srsName="urn:ogc:def:crs:OGC:1.3:CRS84">
        <gml:pos>-61.585973 16.331189</gml:pos>
        <gml:pos>-61.52537 16.400376</gml:pos>
      </lonLatEnvelope>
    </CoverageOfferingBrief>
  </ContentMetadata>
</WCS_Capabilities>

VERSION

This parameter allows to specify the version of the service to use. Currently, the version values is not internally used and always fallback to 1.1.1.

3.4.2. DescribeCoverage

This request allows to retrieve additional information about coverages like the format of the underlying datasource, the number of bands, … Standard parameters for the DescribeCoverage request according to the OGC WCS 1.1.1 specifications:

Paramètre	Requis	Description
SERVICE	Oui	Name of the service (WCS)
REQUEST	Oui	Name of the request (DescribeCoverage)
VERSION	Non	Version du service
COVERAGE	Non	Specify coverage layers (WCS 1.0.0)
IDENTIFIER	Non	Specify coverage layers (WCS 1.1.1)

Outre les paramètres standard, QGIS prend en charge les paramètres suivants :

Paramètre	Requis	Description
MAP	Oui	Fichier du projet QGIS

The XML document for a 3 bands GeoTIFF raster layer looks like:

<CoverageDescription xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.opengis.net/wcs" xmlns:gml="http://www.opengis.net/gml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" updateSequence="0" version="1.0.0" xsi:schemaLocation="http://www.opengis.net/wcs http://schemas.opengis.net/wcs/1.0.0/describeCoverage.xsd">
  <CoverageOffering>
    <name>T20QPD_20171123T144719_TCI</name>
    <label>T20QPD_20171123T144719_TCI</label>
    <lonLatEnvelope srsName="urn:ogc:def:crs:OGC:1.3:CRS84">
      ...
    </lonLatEnvelope>
    <domainSet>
      ...
    </domainSet>
    <rangeSet>
      <RangeSet>
        <name>Bands</name>
        <label>Bands</label>
        <axisDescription>
          <AxisDescription>
            <name>bands</name>
            <label>bands</label>
            <values>
              <singleValue>1</singleValue>
              <singleValue>2</singleValue>
              <singleValue>3</singleValue>
            </values>
          </AxisDescription>
        </axisDescription>
      </RangeSet>
    </rangeSet>
    <supportedCRSs>
    ...
    </supportedCRSs>
    <supportedFormats nativeFormat="raw binary">
      <formats>GeoTIFF</formats>
    </supportedFormats>
  </CoverageOffering>
</CoverageDescription>

COVERAGE

This parameter, defined in WCS 1.0.0, allows to specify the layers to query for additional information. Names have to be separated by a comma.

In addition, QGIS Server introduced an option to select layers by its short name. The short name of a layer may be configured through Properties ► Metadata in layer menu. If the short name is defined, then it’s used by default instead of the layer’s name:

http://localhost/qgisserver?
SERVICE=WCS
&REQUEST=DescribeCoverage
&COVERAGE=mylayer1name,mylayer2shortname

Note

COVERAGE is mandatory if IDENTIFIER is not set.

IDENTIFIER

This parameter replaces the COVERAGE parameter in WCS 1.1.1. But QGIS Server does not filter according to the VERSION parameter so IDENTIFIER and COVERAGE have the same effect.

Note

IDENTIFIER is mandatory if COVERAGE is not set. If both IDENTIFIER and COVERAGE parameters are defined, COVERAGE is always used in priority.

3.4.3. GetCoverage

This request allows to retrieve the coverage according to specific constraints like the extent or the CRS. Standard parameters for the DescribeCoverage request according to the OGC WCS 1.1.1 specifications:

Paramètre	Requis	Description
SERVICE	Oui	Name of the service (WCS)
REQUEST	Oui	Name of the request (GetCoverage)
VERSION	Non	Version du service
COVERAGE	Non	Specify coverage layers (WCS 1.0.0)
IDENTIFIER	Non	Specify coverage layers (WCS 1.1.1)
WIDTH	Oui	Width of the response in pixels
HEIGHT	Oui	Height of the response in pixels
BBOX	Oui	Map extent in CRS units
CRS	Oui	Coordinate reference system of the extent
RESPONSE_CRS	Non	Coordinate reference system of the response

Outre les paramètres standard, QGIS prend en charge les paramètres suivants :

Paramètre	Requis	Description
MAP	Oui	Fichier du projet QGIS

BBOX

This parameter allows to specify the map extent in the units of the current CRS. Coordinates have to be separated by a comma. The BBOX parameter is formed like minx,miny,maxx,maxy.

Exemple d’URL :

http://localhost/qgisserver?
SERVICE=WCS
&REQUEST=GetCoverage
&IDENTIFIER=T20QPD_20171123T144719_TCI
&BBOX=647533,1805950,660987,1813940
&CRS=EPSG:32620

CRS

This parameter allows to indicate the Spatial Reference System of the BBOX parameter and has to be formed like EPSG:XXXX.

RESPONSE_CRS

This parameter allows to indicate the output response Spatial Reference System and has to be formed like EPSG:XXXX. The CRS of the corresponding coverage layer is used by default.

WIDTH

This parameter allows to specify the width in pixels of the output image. The resolution of the response image depends on this value.

HEIGHT

This parameter allows to specify the height in pixels of the output image. The resolution of the response image depends on this value.