WPS Operations

WPS defines three operations for the discovery and execution of geospatial processes. The operations are:

  • GetCapabilities
  • DescribeProcess
  • Execute

GetCapabilities

The GetCapabilities operation requests details of the service offering, including service metadata and metadata describing the available processes. The response is an XML document called the capabilities document.

The required parameters, as in all OGC GetCapabilities requests, are service=WPS, version=1.0.0 and request=GetCapabilities.

An example of a GetCapabilities request is:

http://localhost:8080/geoserver/ows?
  service=WPS&
  version=1.0.0&
  request=GetCapabilities

DescribeProcess

The DescribeProcess operation requests a description of a WPS process available through the service.

The parameter identifier specifies the process to describe. Multiple processes can be requested, separated by commas (for example, identifier=JTS:buffer,gs:Clip). At least one process must be specified.

Note

As with all OGC parameters, the keys (request, version, etc) are case-insensitive, and the values (GetCapabilities, JTS:buffer, etc.) are case-sensitive. GeoServer is generally more relaxed about case, but it is best to follow the specification.

The response is an XML document containing metadata about each requested process, including the following:

  • Process name, title and abstract
  • For each input and output parameter: identifier, title, abstract, multiplicity, and supported datatype and format

An example request for the process JTS:buffer is:

http://localhost:8080/geoserver/ows?
  service=WPS&
  version=1.0.0&
  request=DescribeProcess&
  identifier=JTS:buffer

The response XML document contains the following information:

Title “Buffers a geometry using a certain distance”
Inputs

geom: “The geometry to be buffered” (geometry, mandatory)

distance: “The distance (same unit of measure as the geometry)” (double, mandatory)

quadrant segments: “Number of quadrant segments. Use > 0 for round joins, 0 for flat joins, < 0 for mitred joins” (integer, optional)

capstyle: “The buffer cap style, round, flat, square” (literal value, optional)
Output formats One of GML 3.1.1, GML 2.1.2, or WKT

Execute

The Execute operation is a request to perform the process with specified input values and required output data items. The request may be made as either a GET URL, or a POST with an XML request document. Because the request has a complex structure, the POST form is more typically used.

The inputs and outputs required for the request depend on the process being executed. GeoServer provides a wide variety of processes to process geometry, features, and coverage data. For more information see the section WPS Processes.

Below is an example of a Execute POST request. The example process (JTS:buffer) takes as input a geometry geom (in this case the point POINT(0 0)), a distance (with the value 10), a quantization factor quadrantSegments (here set to be 1), and a capStyle (specified as flat). The <ResponseForm> element specifies the format for the single output result to be GML 3.1.1.

<?xml version="1.0" encoding="UTF-8"?>
<wps:Execute version="1.0.0" service="WPS" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wps/1.0.0" xmlns:wfs="http://www.opengis.net/wfs" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:wcs="http://www.opengis.net/wcs/1.1.1" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsAll.xsd">
  <ows:Identifier>JTS:buffer</ows:Identifier>
  <wps:DataInputs>
    <wps:Input>
      <ows:Identifier>geom</ows:Identifier>
      <wps:Data>
        <wps:ComplexData mimeType="application/wkt"><![CDATA[POINT(0 0)]]></wps:ComplexData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>distance</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>10</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>quadrantSegments</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>1</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>capStyle</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>flat</wps:LiteralData>
      </wps:Data>
    </wps:Input>
  </wps:DataInputs>
  <wps:ResponseForm>
    <wps:RawDataOutput mimeType="application/gml-3.1.1">
      <ows:Identifier>result</ows:Identifier>
    </wps:RawDataOutput>
  </wps:ResponseForm>
</wps:Execute>

The process performs a buffer operation using the supplied inputs, and returns the outputs as specified. The response from the request is (with numbers rounded for clarity):

<?xml version="1.0" encoding="utf-8"?>
<gml:Polygon xmlns:sch="http://www.ascc.net/xml/schematron"
 xmlns:gml="http://www.opengis.net/gml"
 xmlns:xlink="http://www.w3.org/1999/xlink">
  <gml:exterior>
    <gml:LinearRing>
      <gml:posList>
        10.0 0.0
        0.0 -10.0
        -10.0 0.0
        0.0 10.0
        10.0 0.0
      </gml:posList>
    </gml:LinearRing>
  </gml:exterior>
</gml:Polygon>

For help in generating WPS requests you can use the built-in interactive WPS Request Builder.