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Browse SpaceThe WFS GetNearest Plug-in is used to get a feature from the WFS that is nearest to a given point. Along with the feature, the distance and bearing is also returned as new feature attributes.
Installing the Plug-in
To install the plug-in, copy the plug-in JAR (ORCI-GetNearestPlugin-1.0-jar) to geoserver's WEB-INF/lib directory. Upon startup, geoserver will automatically detect the plugin and add the GetNearest request to its WFS service.
WFS Request
The GetNearest request takes a few custom parameters:
| Parameter | Description |
|---|---|
| Point | The point from which to find the nearest feature. |
| MaxRange | The maximum search range from the point. |
| Units | The units for the search range. |
Along with these parameters, custom filters may be added to the request as with the GetFeature WFS request.
Sample Request
http://localhost:8080/geoserver/wfs?request=getNearest&service=wfs&version=1.0.0&typename=tiger:pl&PropertyName=tiger:name,lsad_trans
&POINT=-77.51761,37.02235&MAXRANGE=50&UNITS=mi
This request will return the nearest feature from the tiger:pl layer to the point -77.51761,37.02235. The maximum search range is set to 50 miles. This request will return the following feature set.
<wfs:FeatureCollection xsi:schemaLocation="http://www.census.gov http://localhost:8080/geoserver/wfs/DescribeFeatureType?typeName=tiger:pl http://www.opengis.net/wfs http://localhost:8080/geoserver/schemas/wfs/1.0.0/WFS-basic.xsd"> <gml:boundedBy> <gml:Box srsName="http://www.opengis.net/gml/srs/epsg.xml#4326"> <gml:coordinates decimal="." cs="," ts=" "> -77.406378,36.940298 -77.391313,36.956486 </gml:coordinates> </gml:Box> </gml:boundedBy> <gml:featureMember> <tiger:pl fid="pl.302"> <tiger:name>Stony Creek</tiger:name> <tiger:lsad_trans>town</tiger:lsad_trans> <tiger:nearest_distance>7.760402085851028</tiger:nearest_distance> <tiger:nearest_bearing>228.81705674288395</tiger:nearest_bearing> </tiger:pl> </gml:featureMember> </wfs:FeatureCollection>
Notice that two new attributes have been added to the feature.
| Attribute | Description |
|---|---|
| nearest_distance |
This is the distance from the given point to the feature in the units specified in the request. |
| nearest_bearing | This is the compass bearing from the point to the feature in degrees. |
Plug-in Details
The following source files make up the plug-in.
| Classes |
Description |
|---|---|
| FeatureBoundsFeatureCollection | This class is used to return only the attributes of a feature specified on the request (&Property=). |
| GetNearest | This class extends the WFService class and adds the new GetNearest request to the WFS. |
| GetNearestHandler | This class is the SAX Parser handler used to parse the XML request sent in an HTTP POST request. |
| GetNearestKvpReader | This class reads the Key-Value-Pair parameters included on the request URL. |
| GetNearestRequest | This class holds the GetNearest request parameters. |
| GetNearestResponse | This class is responsible for executing the GetNearest request and identifying the nearest feature. |
| GetNearestResponseDelegate | This is an interface defining a general response delegate. |
| GetNearestResponseDelegateProducerSpi | This is an interface defining a general response delegate factory. |
| GetNearestResults | This class holds the response to the GetNearest request. In the case of this request, it will have a single feature. |
| GetNearestXmlReader | This class is the SAX Parser XML reader used to parse the XML request sent in an HTTP POST request. |
| GML2GetNearestResponseDelegate | This is the response delegate responsible for generating GML2 output. |
| GML2GetNearestResponseDelegateFactory | This is the delegate factory for creating the GML2GetNearestResponseDelegate. |
Along with these classes, there are two configuration files.
| Configuration file |
Description |
|---|---|
| com.orci.geoserver.wfs.getnearest.GetNearestResponseDelegateProducerSpi | This file registers the delegate response factories. This file is saved in the META-INF/services directory of the JAR. |
| applicationContext.xml | This file registers the GetNearest request with the WFS service. This file is saved in the root directory of the JAR. |