Hi Martin and Andrea, sorry for the late of my reply but I've had some troubles in these days and I was out of office.
First of all I try to explain what I'd like to do with my WPS process. I've tried to reply the steps using QGIS on the same data (shapefile) and capture images: 1) select a state (Texas): figure SelectedState-TX.jpg 2) calculate a buffer around the selected state: figure BufferAroundSelectedStateTX.jpg 3) intersect this buffer with the state layer and find the states that interscet the buffer: figure StateIntersect.jpg Note the I'd like to use the buffer to intersect other layers too. I hope in this manner could be clear my goal. So can I obtain my goal using my original WPS process? Other ways? The only thing that I've to do is update my GeoServer? Here you are the build infomation about my GeoServer: - Version 2.1-SNAPSHOT - Subversion Revision 16780 - Build Date 22-Feb-2012 05:02 - GeoTools Version 2.7-SNAPSHOT (rev 38575) Another question: the gs:CollectGeometries works fine but if I've a "real" layers with a lot of features (> 1000), is good too? Thank you in advance... Cesare 2012/6/22 Martin Davis <mda...@opengeo.org> > > > On Thu, Jun 21, 2012 at 1:05 PM, Andrea Aime <andrea.a...@geo-solutions.it > > wrote: > >> On Thu, Jun 21, 2012 at 8:17 PM, Martin Davis <mda...@opengeo.org> wrote: >> >>> The reason for the exception is that the JTS intersection operation only >>> works on valid geometries. Unfortunately the output of the >>> gs:CollectGeometries process may not be valid in the case where it is >>> collecting a set of Polygons. This is because polygons which are adjacent >>> to each other or which overlap do not form valid MultiPolygons. Both of >>> these situations occur in your process (the input states are adjacent, and >>> the buffers will overlap). >> >> >> The current version of collectGeometries now does a union before >> returning polygon collections, I guess you haven't used it in a few months, >> the >> change has been made in March (http://jira.codehaus.org/browse/GEOT-4077) >> >> However this might explain why Cesare's case is not working, I believe he >> has a 2.1.3 installed. >> > > Oh, right, I see that now. It should probably use the newish JTS > Geometry.union() rather than buffer(0) - it's faster for large datasets. > >> >> >>> >>> Actually the buffer operation should work with any kind of input, and >>> produce a valid polygonal output. So the problem is due to collecting the >>> STATES polygons together and trying to use that in JTS:intersection. >>> >>> In fact, the JTS:intersection operation is not designed to work on >>> collections of geometries anyway. >>> >> >> The gs:CollectGeometries process made sure to build a type specific >> collection for that very reason, you will get back >> a GeometryCollection only if the collected geometries are etherogeneous: >> >> http://svn.osgeo.org/geotools/trunk/modules/library/main/src/main/java/org/geotools/geometry/jts/GeometryCollector.java >> >> Or do you mean that intersecting a Multipolygon against another >> Multipolygon is less robust than an intersection >> between simple polygons? >> > > I mean that in order for the intersection to work, both arguments need to > be valid geometries. In the case of the states collection, this requires > that they be unioned together. The effect of this is to produce a single > polygon (the outline of the US). Then the result of the intersection is > going to be a single polygon. I took a guess that the desire result was > actually a collection of the intersections of the individual state polygons > against the buffer polygon (this is the most common reason for this kind of > processing, in my experience). > >> >> >>> >>> -- > Martin Davis > OpenGeo - http://opengeo.org > Expert service straight from the developers. > > -- Cesare Gerbino
<<attachment: SelectedState-TX.jpg>>
<<attachment: BufferAroundSelectedStateTX.jpg>>
<<attachment: StateIntersect.jpg>>
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