7.1. WCS Map Service#

WCS - Web Coverage Service, WCS is a specification for sharing geospatial data in the form of “Coverage” on the Web as defined by the OGC. The so-called “Coverage” refers to data that can return the value of any specified point in its space-time domain, and its form is easy to input into the model for use. The WCS service realizes the sharing of raster image datasets in the form of “Coverage”.

7.1.1. Mapfile definition#

As in WMS and WFS support, WCS publishing is enabled by adding certain metadata key/value pairs to the .map file.

MapServer targets only layers that meet the following conditions and includes them in its WCS function:

the data source is a raster and can be processed using GDAL (eg GeoTIFF, Erdas Imaging, …);
the layer name must be set;
the layer type is set to RASTER ;
Web metadata or layer metadata wcs_enable_request must be set;
Web metadata wcs_label must be set;
must set layer metadata wcs_label , wcs_rangeset_name , wcs-rangeset-label ;
Layers can be served via WCS (see MS RFC 67);
The layer projection must be set, even if the projection is set at the map level.

Take a look at the Mapfile used in this section:

MAP
    EXTENT -180 -90 180 90
    SIZE 600 300
    SHAPEPATH "/gdata"
    OUTPUTFORMAT
        NAME "GEOTIFF_16"
        DRIVER "GDAL/GTiff"
        MIMETYPE "image/tiff"
        IMAGEMODE FLOAT32
        EXTENSION "tif"
    END
    WEB
        IMAGEPATH "/owg/ms_tmp/"
        IMAGEURL "/ms_tmp/"
        METADATA
            "wcs_onlineresource" "http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map"
            "wcs_keywordlist" "wcs,test"
            "wcs_enable_request" "*"
        END
    END
    PROJECTION
        "init=epsg:4326"
    END
    LAYER
        METADATA
            "wcs_keywordlist" "land, shallow, topo, world"
        END
        NAME "world-img"
        DATA "land_shallow_topo_8192.tif"
        STATUS OFF
        TYPE RASTER
        PROJECTION
            "init=epsg:4326"
        END
    END
END

7.1.2. GetCapabilities request#

As in WMS and WFS, you can also use GetCapabilities to view the capabilities of WCS:

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=2.0.1&REQUEST=GetCapabilities

Parse the parameters using Python:

>>> [print(x) for x  in url.split('&')]
http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map
SERVICE=WCS
VERSION=2.0.1
REQUEST=GetCapabilities

View the output results in XML format. Only the parts related to version are shown here:

<ows:ServiceType codeSpace="OGC">OGC WCS</ows:ServiceType>
<ows:ServiceTypeVersion>2.0.1</ows:ServiceTypeVersion>
<ows:ServiceTypeVersion>1.1.1</ows:ServiceTypeVersion>
<ows:ServiceTypeVersion>1.0.0</ows:ServiceTypeVersion>
<ows:Profile>http://www.opengis.net/spec/WCS/2.0/conf/core</ows:Profile>

You can see that the versions of WCS are:

2.0.1
1.1.1
1.0.0

7.1.3. DescribeCoverage request#

The DescribeCoverage request lists more information about a specific coverage product.

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=2.0.1&REQUEST=DescribeCoverage&COVERAGEID=world-img

The parameters are described as follows:

>>> [print(x) for x  in url.split('&')]
http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map
SERVICE=WCS
VERSION=2.0.1
REQUEST=DescribeCoverage
COVERAGEID=world-img

The parameters vary greatly between different versions, and the returned results are also different. You can open the link to have a look at it:

WFS 1.0.0:

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=1.0.0&REQUEST=DescribeCoverage&COVERAGE=world-img

Parse the URL:

>>> [print(idx, x) for idx, x  in enumerate(url.split('&'))]
http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map
SERVICE=WCS
VERSION=1.0.0
REQUEST=DescribeCoverage
COVERAGE=world-img

WFS 1.1.1:

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=1.1.1&REQUEST=DescribeCoverage&IDENTIFIERS=world-img

Parse the URL:

>>> [print(idx, x) for idx, x  in enumerate(url.split('&'))]
http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map
SERVICE=WCS
VERSION=1.1.1
REQUEST=DescribeCoverage
IDENTIFIERS=world-img

7.1.4. Usage of GetCoverage#

GetCoverage returns data, which is raster data. Since the request cannot specify the name and suffix of the file at this time, the file can be downloaded and saved, and modified into a file with .tif as the suffix. This file has geospatial information.

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=world-img&FORMAT=image/tiff&BOUNDINGBOX=43,33,44,34,urn:ogc:def:crs:EPSG::4326

The parameters are decomposed as follows:

>>> [print(idx, x) for idx, x  in enumerate(url.split('&'))]
http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map
SERVICE=WCS
VERSION=1.1.0
REQUEST=GetCoverage
IDENTIFIER=world-img
FORMAT=image/tiff
BOUNDINGBOX=43,33,44,34,urn:ogc:def:crs:EPSG::4326

GetCoverage return image#

GetCoverage can also directly return the image, just modify format=image/png . However, it should be noted that the returned image must be returned by a separate request in the web, and cannot be used in the web page as an <image> object.

The following is an example, the picture in the web page, which cannot be displayed here. But by “right click” -> “view image”, you can see that it is a picture.

http://webgis.pub/cgi-bin/mapserv?map=/owg/mfw8.map&SERVICE=WCS&VERSION=1.1.0&REQUEST=GetCoverage&IDENTIFIER=world-img&FORMAT=image/tiff&BOUNDINGBOX=33,70,54,135,urn:ogc:def:crs:EPSG::4326&format=image/png

WCS Map Service

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