For the udig "reshape" operation that does the same cql thing you are refering to I used the first feature in the source collection to determine the result type. Not perfect but there you go.
in the past when talking about setting up a "feature chaining" (similar to a jai image processing chain) we talked about setting up two execution paths - one for description and one for data. Since that time our expression system actually stands a chance of supporting that. So to cover description: - return a MultiPolygon.class when passed a Point.class And then the usual value execution path: - return a MultiPolygon object when passed a Point object. You could also consider using an GeometryDescriptor and getting back a GeometryDescriptor? Jody On 27/07/2010, at 6:32 PM, Andrea Aime wrote: > Hi, > today I was trying to create a process that would make > up for some limitations of the WFS GetFeature operation, > in particular the inability to compute on the fly new > attribute. > I'd like to be able to define new attribute in the > returned collection as: > > <ecql expression> as newname > > There is however a big catch in all of this: how do > I create the target schema? > I know the new attribute name, but not its type. > For example, given: > > buffer(the_geom, 20) as bufferedgeom > > how do I get to know it's going to be a Geometry? > The filter function implementations offer nothing > about their return type. > > And, correct me if I'm wrong, without a proper schema > it's not possible to drive a xml encoding or a shapefile > encoding. > > A silly approach could be to run the new attributes against > the first feature and see what type the transformed object > is, but that would fall apart if the_geom is null for that > attribute. Or one could make it go through all of the > input features, serialize the results to avoid recomputing it, > and try to summarize the result type by inspection of all > results. Which would still fail if all of the attributes > involved in the transformation are null... > > Hmmm.... bright ideas, suggestions? > > Cheers > Andrea > > ------------------------------------------------------------------------------ > The Palm PDK Hot Apps Program offers developers who use the > Plug-In Development Kit to bring their C/C++ apps to Palm for a share > of $1 Million in cash or HP Products. Visit us here for more details: > http://ad.doubleclick.net/clk;226879339;13503038;l? > http://clk.atdmt.com/CRS/go/247765532/direct/01/ > _______________________________________________ > Geotools-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/geotools-devel ------------------------------------------------------------------------------ The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://ad.doubleclick.net/clk;226879339;13503038;l? http://clk.atdmt.com/CRS/go/247765532/direct/01/ _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
