8.9. KNearestNeighborSearchProcess

The KNearestNeighborSearchProcess performs a K-nearest-neighbor search on a feature collection using a second feature collection as input. It returns k neighbors for each point in the input data set. Note that if a feature is the nearest neighbor of multiple points in the input data set, it is returned only once. It accepts the following parameters:

Parameter	Description
inputFeatures	Input feature collection. The geometries of the features defines the KNN search
dataFeatures	The data set to query for neighbors
numDesired	k, number of nearest neighbors to return
estimatedDistance	Estimate of the distance in meters for the k-th nearest neighbor, used for the initial query window
maxSearchDistance	Maximum search distance in meters, used to prevent runaway queries of the entire data set

8.9.1. K-Nearest-Neighbor Example

The following XML shows an example KNN request. It is chained with a Query process (see Chaining Processes), in order to avoid returning the query features as data.

<?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: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>geomesa:KNearestNeighborSearch</ows:Identifier>
  <wps:DataInputs>
    <wps:Input>
      <ows:Identifier>inputFeatures</ows:Identifier>
      <wps:Reference mimeType="text/xml; subtype=wfs-collection/1.0" xlink:href="http://geoserver/wps" method="POST">
        <wps:Body>
          <wps:Execute version="1.0.0" service="WPS">
            <ows:Identifier>geomesa:Query</ows:Identifier>
            <wps:DataInputs>
              <wps:Input>
                <ows:Identifier>features</ows:Identifier>
                <wps:Reference mimeType="text/xml; subtype=wfs-collection/1.0" xlink:href="http://geoserver/wfs" method="POST">
                  <wps:Body>
                    <wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:cabs="cabs">
                      <wfs:Query typeName="cabs:Cabs_features"/>
                    </wfs:GetFeature>
                  </wps:Body>
                </wps:Reference>
              </wps:Input>
              <wps:Input>
                <ows:Identifier>filter</ows:Identifier>
                <wps:Data>
                  <wps:ComplexData mimeType="text/plain; subtype=cql"><![CDATA[CabId = 367152240]]></wps:ComplexData>
                </wps:Data>
              </wps:Input>
            </wps:DataInputs>
            <wps:ResponseForm>
              <wps:RawDataOutput mimeType="text-xml; subtype=wfs-collection/1.0">
                <ows:Identifier>result</ows:Identifier>
              </wps:RawDataOutput>
            </wps:ResponseForm>
          </wps:Execute>
        </wps:Body>
      </wps:Reference>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>dataFeatures</ows:Identifier>
      <wps:Reference mimeType="text/xml; subtype=wfs-collection/1.0" xlink:href="http://geoserver/wps" method="POST">
        <wps:Body>
          <wps:Execute version="1.0.0" service="WPS">
            <ows:Identifier>geomesa:Query</ows:Identifier>
            <wps:DataInputs>
              <wps:Input>
                <ows:Identifier>features</ows:Identifier>
                <wps:Reference mimeType="text/xml; subtype=wfs-collection/1.0" xlink:href="http://geoserver/wfs" method="POST">
                  <wps:Body>
                    <wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:cabs="cabs">
                      <wfs:Query typeName="cabs:Cabs_features"/>
                    </wfs:GetFeature>
                  </wps:Body>
                </wps:Reference>
              </wps:Input>
              <wps:Input>
                <ows:Identifier>filter</ows:Identifier>
                <wps:Data>
                  <wps:ComplexData mimeType="text/plain; subtype=cql"><![CDATA[NOT(CabId = 367152240)]]></wps:ComplexData>
                </wps:Data>
              </wps:Input>
            </wps:DataInputs>
            <wps:ResponseForm>
              <wps:RawDataOutput mimeType="text-xml; subtype=wfs-collection/1.0">
                <ows:Identifier>result</ows:Identifier>
              </wps:RawDataOutput>
            </wps:ResponseForm>
          </wps:Execute>
        </wps:Body>
      </wps:Reference>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>numDesired</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>1</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>estimatedDistance</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>50</wps:LiteralData>
      </wps:Data>
    </wps:Input>
    <wps:Input>
      <ows:Identifier>maxSearchDistance</ows:Identifier>
      <wps:Data>
        <wps:LiteralData>1000</wps:LiteralData>
      </wps:Data>
    </wps:Input>
  </wps:DataInputs>
  <wps:ResponseForm>
    <wps:RawDataOutput mimeType="application/json">
      <ows:Identifier>result</ows:Identifier>
    </wps:RawDataOutput>
  </wps:ResponseForm>
</wps:Execute>

Assuming the above XML is in a file named KNNProcess_wps.xml, it can be invoked with the following curl to GeoServer:

curl -v -u admin:geoserver -H "Content-Type: text/xml" -d@KNNProcess_wps.xml localhost:8080/geoserver/wps