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.

Especificações:

Standard requests provided by QGIS Server:

Solicitação	Descrição
GetCapabilities	Returns XML metadata with information about the server
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:

Parâmetros	Requerido	Descrição
SERVICE	Sim	Name of the service (WCS)
REQUEST	Sim	Name of the request (GetCapabilities)
VERSION	Não	Versão do serviço

Além dos padrões, o QGIS Server suporta os seguintes parâmetros extras:

Parâmetros	Requerido	Descrição
MAP	Sim	Arquivo de projeto QGIS

Exemplo de URL:

http://localhost/qgis_server?
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>

VERSÃO

Este parâmetro permite especificar a versão do serviço a ser utilizada. Atualmente, os valores de versão não são usados internamente e sempre retornam para 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:

Parâmetros	Requerido	Descrição
SERVICE	Sim	Name of the service (WCS)
REQUEST	Sim	Name of the request (DescribeCoverage)
VERSION	Não	Versão do serviço
COVERAGE	Não	Specify coverage layers (WCS 1.0.0)
IDENTIFIER	Não	Especificar camadas de cobertura (WCS 1.1.1)

Além dos padrões, o QGIS Server suporta os seguintes parâmetros extras:

Parâmetros	Requerido	Descrição
MAP	Sim	Arquivo de projeto QGIS

O documento XML para uma camada raster GeoTIFF de 3 bandas se parece com:

<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>

COBERTURA

Este parâmetro, definido no WCS 1.0.0, permite especificar as camadas a serem consultadas por informações adicionais. Os nomes devem ser separados por vírgula.

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

Nota

COVERAGE is mandatory if IDENTIFIER is not set.

IDENTIFICADOR

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.

Nota

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:

Parâmetros	Requerido	Descrição
SERVICE	Sim	Name of the service (WCS)
REQUEST	Sim	Name of the request (GetCoverage)
VERSION	Não	Versão do serviço
COVERAGE	Não	Specify coverage layers (WCS 1.0.0)
IDENTIFIER	Não	Especificar camadas de cobertura (WCS 1.1.1)
WIDTH	Sim	Largura da resposta em pixels
HEIGHT	Sim	Altura da resposta em pixels
BBOX	Sim	Extensão do mapa em unidades SRC
CRS	Sim	Sistema de Referência de Coordenadas da extensão
RESPONSE_CRS	Não	Sistema de referência de coordenadas da resposta

Além dos padrões, o QGIS Server suporta os seguintes parâmetros extras:

Parâmetros	Requerido	Descrição
MAP	Sim	Arquivo de projeto 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.

Exemplo de URL:

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

SRC

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.

LARGURA

Este parâmetro permite especificar a largura em pixels da imagem de saída. A resolução da imagem de resposta depende desse valor.

ALTURA

Este parâmetro permite especificar a altura em pixels da imagem de saída. A resolução da imagem de resposta depende desse valor.

../../../_images/server_wcs_getcoverage_width_height.png — Fig. 3.22 From left to right: `WIDTH=20&HEIGHT=20`, `WIDTH=50&HEIGHT=50`, `WIDTH=100&HEIGHT=100`