Your WFS query won't work because <Intersection> is not a supported
operation in the OGC Filter Encoding spec. (<Intersects> is, however,
which is why the initial query worked.) In general, WFS supports
expressing *filters* for data, but not *manipulation* of the retrieved
data. So it is not an option for the kind of processing that you want to
do. (Perhaps this will be improved in a new version of the spec, or by
some GeoServer-specific enhancements...)
As for the WPS query, the syntax looks fine. What you are seeing is an
empty result being returned. Are you sure that the "communi_ita" dataset
has features in the are that you are trying to intersect?
If you are only intersecting with a rectangle, you may also want to try
gs:Clip or gs:RectangularClip - they are optimized for clipping feature
geometry to a given polygon and rectangle.
As for union, if what you are wanting to do is to geometrically union all
the data from a layer unfortunately there isn't currently a process which
will accomplish this. It's quite possible to create such a process in Java
with fairly small effort, however - you could try and do this yourself, or
consider funding someone to do this.
On Mon, Dec 10, 2012 at 8:09 AM, Paolo Crosato <
[email protected]> wrote:
> Hi,
>
> I'm trying to perform by use of Geoserver the equivalent of the Postgis
> ST_intersection and ST_Union functions. The server I'm working with is
> the os indipendent binary with jetty.
>
> In the first case, I need to compute the intersection between a polygon
> (a rectangle) and a postgis table published as a WFS vector layer via
> Geoserver. The simple intersects, which I performed succesfully, is not
> sufficient since I need to minimize the information transimitted over
> the network, because the application will run on mobile clients.
> First I tried with a simple WFS request, since I found on the
> GetCapabilities response for the WFS service that the "intersection"
> function was supported, as intersects is. So I tried this simple XML,
> which works with intersects:
>
> <wfs:GetFeature service="WFS" version="1.1.0"
> xmlns:topp="http://www.openplans.org/topp";
> xmlns:wfs="http://www.opengis.net/wfs";
> xmlns="http://www.opengis.net/ogc";
> xmlns:gml="http://www.opengis.net/gml";
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
> xsi:schemaLocation="http://www.opengis.net/wfs
> http://schemas.opengis.net/wfs/1.1.0/wfs.xsd";>
> <wfs:Query typeName="navteq:geoserver_comuni">
> <Filter>
> <Intersection>
> <PropertyName>geom</PropertyName>
> <gml:Polygon srsName="urn:ogc:def:crs:EPSG:6.9:4326">
> <gml:exterior>
> <gml:LinearRing>
> <gml:posList>45.429299 11.82518 45.429299 12.540665 45.77327
> 12.540665 45.77327 11.82518 45.429299 11.82518</gml:posList>
> </gml:LinearRing>
> </gml:exterior>
> </gml:Polygon>
> </Intersection>
> </Filter>
> </wfs:Query>
> </wfs:GetFeature>
>
> However, I got a "Unable to find function Intersection" response from
> the server.
> I did some research, and found the preferred way to do this kind of
> computation seems to be using a WPS approach, so I installed the WPS
> extension and looked for some examples.
> I tried this example, which was assembled by a mixture of the WPS
> builder and an example I found on this thread:
>
> http://osgeo-org.1560.n6.nabble.com/Geoserver-2-2-Insertection-with-buffer-td5009029.html
> This is the code I tried:
>
> <?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>gs:IntersectionFeatureCollection</ows:Identifier>
> <wps:DataInputs>
> <wps:Input>
> <ows:Identifier>first feature collection</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>gs:Feature</ows:Identifier>
> <wps:DataInputs>
> <wps:Input>
> <ows:Identifier>geometry</ows:Identifier>
> <wps:Data>
> <wps:ComplexData
> mimeType="application/wkt"><![CDATA[POLYGON((45.429299
> 11.82518,45.429299 12.540665,45.77327 12.540665,45.77327
> 11.82518,45.429299 11.82518))]]></wps:ComplexData>
> </wps:Data>
> </wps:Input>
> <wps:Input>
> <ows:Identifier>crs</ows:Identifier>
> <wps:Data>
> <wps:LiteralData>EPSG:4326</wps:LiteralData>
> </wps:Data>
> </wps:Input>
> <wps:Input>
> <ows:Identifier>typeName</ows:Identifier>
> <wps:Data>
> <wps:LiteralData>buf</wps:LiteralData>
> </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>second feature collection</ows:Identifier>
> <wps:Reference mimeType="text/xml"
> xlink:href="http://geoserver/wfs"; method="POST">
> <wps:Body>
> <wfs:GetFeature service="WFS" version="1.0.0"
> outputFormat="GML2" xmlns:navteq="navteq">
> <wfs:Query typeName="navteq:comuni_ita"/>
> </wfs:GetFeature>
> </wps:Body>
> </wps:Reference>
> </wps:Input>
> <wps:Input>
> <ows:Identifier>intersectionMode</ows:Identifier>
> <wps:Data>
> <wps:LiteralData>INTERSECTION</wps:LiteralData>
> </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>
>
> I thought this would give me back the set of intersecting geometries,
> however I got this response, seems to be the bbox I put as input:
> <?xml version="1.0" encoding="UTF-8"?>
> <wfs:FeatureCollection xmlns:ogc="http://www.opengis.net/ogc";
> xmlns:gml="http://www.opengis.net/gml";
> xmlns:wfs="http://www.opengis.net/wfs";>
> <gml:boundedBy>
> <gml:Box srsName="http://www.opengis.net/gml/srs/epsg.xml#4326";>
>
> <gml:coord><gml:X>45.429299</gml:X><gml:Y>11.82518</gml:Y></gml:coord><gml:coord><gml:X>45.77327</gml:X><gml:Y>12.540665</gml:Y></gml:coord></gml:Box>
> </gml:boundedBy>
> </wfs:FeatureCollection>
>
> I'm pretty new to Geoserver, so I've got no big clues on what to do now.
> 1) Is WPS and gs:IntersectionFeatureCollection the right way to do this,
> or is something wrong with the WFS intersection example I tried before?
> 2) Could anyone give me a clue on what is wrong with my WPS example?
> 3) I need to do the same with ST_Union, I gave a look at the description
> of gs:union, however it seems to work only with 2 single features, while
> I'd need to perform an aggregate
> function on an entire set of geometries, based on attributes.
>
> The most important issue for me, however, is that I'm trying to use
> Geoserver because I'd like to put a layer between the database and the
> application running on the client.
> I could do the same with a java webapp performing only the operations I
> need, basicly mapping them to calls to postgis functions, but I'd really
> like to avoid all the coding,
> mainly because we already have a lot of custom code to mantain. I'd like
> to switch from implementing code to wiring applications in an
> infrastructure.
> Is Geoserver the right tool to use from this perspective, or should I
> code the "transactional" operations in Java and use Geoserver just for
> simple WMS and WFS requests?
>
> Thank you in advance for any response.
>
> Regards.
>
> --
> Paolo Crosato
>
>
>
>
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--
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OpenGeo - http://opengeo.org
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