WCS requests for multidimensional coverages

WCS 2.0.1 provides capabilities to access multidimensional data. Requests like the GetCapabilities seen in the previous section or the DescribeCoverage provided below, allow to get information about the extent of the whole coverage.

WCS 2.0 Sample Requests

DescribeCoverage

KVP Encoding

Single Coverage

http://localhost:8083/geoserver/ows?service=WCS&version=2.0.1&request=DescribeCoverage&coverageId=geosolutions__NO2

The request will download an XML containing the details of the multidimensional coverage.

  • The BoundedBy is represented by an EnvelopeWithTimePeriod

    <gml:boundedBy>
        <gml:EnvelopeWithTimePeriod srsName="http://www.opengis.net/def/crs/EPSG/0/4326" axisLabels="Lat Long elevation time" uomLabels="Deg Deg m s" srsDimension="3">
            <gml:lowerCorner>44.96875 4.9375 10.0</gml:lowerCorner>
            <gml:upperCorner>50.96875 14.9375 2500.0</gml:upperCorner>
            <gml:beginPosition>2013-03-01T00:00:00.000Z</gml:beginPosition>
            <gml:endPosition>2013-03-02T23:00:00.000Z</gml:endPosition>
        </gml:EnvelopeWithTimePeriod>
    </gml:boundedBy>
    
  • The TimeDomain reports the list of the available TimePosition’s

    <wcsgs:TimeDomain default="2013-03-02T23:00:00.000Z">
       <gml:TimeInstant gml:id="geosolutions__NO2_td_0">
          <gml:timePosition>2013-03-01T00:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       <gml:TimeInstant gml:id="geosolutions__NO2_td_1">
          <gml:timePosition>2013-03-01T01:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       <gml:TimeInstant gml:id="geosolutions__NO2_td_2">
          <gml:timePosition>2013-03-01T02:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       <gml:TimeInstant gml:id="geosolutions__NO2_td_3">
          <gml:timePosition>2013-03-01T03:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       <gml:TimeInstant gml:id="geosolutions__NO2_td_4">
          <gml:timePosition>2013-03-01T04:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       <gml:TimeInstant gml:id="geosolutions__NO2_td_5">
          <gml:timePosition>2013-03-01T05:00:00.000Z</gml:timePosition>
       </gml:TimeInstant>
       ....
    </wcsgs:TimeDomain>
    
  • The ElevationDomain reports the list values for the available elevations

    <wcsgs:ElevationDomain uom="m" default="10.0">
       <wcsgs:SingleValue>10.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>35.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>75.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>125.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>175.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>250.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>350.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>450.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>550.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>700.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>900.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>1250.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>1750.0</wcsgs:SingleValue>
       <wcsgs:SingleValue>2500.0</wcsgs:SingleValue>
    </wcsgs:ElevationDomain>
    
  • The DimensionDomain reports the list of the available dimensions for this coverage

    <wcsgs:DimensionDomain name="UPDATED" default="2013-04-08T07:40:29.061Z">
      <gml:TimeInstant gml:id="geosolutions__NO2_dd_0">
       <gml:timePosition>2013-04-08T07:40:29.061Z</gml:timePosition>
      </gml:TimeInstant>
      <gml:TimeInstant gml:id="geosolutions__NO2_dd_0">
       <gml:timePosition>2013-04-08T07:41.597Z</gml:timePosition>
      </gml:TimeInstant>
    </wcsgs:DimensionDomain>
    <wcsgs:DimensionDomain name="FILEDATE" default="2013-03-01T00:00:00.000Z">
      <gml:TimeInstant gml:id="geosolutions__NO2_dd_0">
       <gml:timePosition>2013-03-01T00:00:00.000Z</gml:timePosition>
      </gml:TimeInstant>
      <gml:TimeInstant gml:id="geosolutions__NO2_dd_0">
       <gml:timePosition>2013-03-02T00:00:00.000Z</gml:timePosition>
      </gml:TimeInstant>
    </wcsgs:DimensionDomain>
    

Those dimension values may be used to perform a getCoverage request in order to get raw data back. WCS 2.0.1 also allows getting raw data from a multidimensional coverage through slicing and trimming:

  • Slicing: allows to specify a single value for a specific dimension
  • Trimming: allows to specify a min-max values range for a specific dimension, as an instance, time, in order to get back all the data available within that range.

GetCoverage

KVP Encoding

The following request will get back a GeoTiff produced on top of raw data defined by this selection:

  • Trimming on latitude [40 -> 50]
  • Trimming on longitude [5 -> 20]
  • Slicing on elevation [350]
  • Slicing on time [2013-03-01T10:00:00.000Z]

GetCoverage request using KVP encoding

http://localhost:8083/geoserver/wcs?request=GetCoverage&service=WCS&version=2.0.1&coverageId=geosolutions__NO2&Format=geotiff&subset=http://www.opengis.net/def/axis/OGC/0/Long(5,20)&subset=http://www.opengis.net/def/axis/OGC/0/Lat(40,50)&subset=http://www.opengis.net/def/axis/OGC/0/elevation(350)&subset=http://www.opengis.net/def/axis/OGC/0/time("2013-03-01T10:00:00.000Z")

The browser should download a geosolutions__NO2.tif containing the requested data.

Trimming on dimensions (except the 2D dimensions such as latitude and logitude) is only supported when the output format properly supports the creation of a dataset containing multiple results, each of them being related to a specific combination of values for the requested dimensions.

Therefore, a NetCDF output format has been developed to achieve this, as explained in the next section.

Default values management

A Default values management logic is applied under these conditions:

  1. The output format doesn’t support multiple results so a single element will be served
  2. The granules are provided by a Structured GridCoverageReader
  3. Some dimensions haven’t been specified in the request

In that case a query will be performed to get a granule matching the specified dimension values. Then the unspecified dimensions values will be set to the values obtained from the returned granule.