I agree with Andrea's view. The problem I guess is not how you do the non preserving generalisation, since I seem to understand you are not interested in it, therefore you can just ignore it. The point is to let room for people that want/can actually do it. An example I can give is turning a line or a polygon into a point at certain resolution levels.
Simone. ------------------------------------------------------- Ing. Simone Giannecchini GeoSolutions S.A.S. Owner - Software Engineer Via Carignoni 51 55041 Camaiore (LU) Italy phone: +39 0584983027 fax: +39 0584983027 mob: +39 333 8128928 http://www.geo-solutions.it http://simboss.blogspot.com/ http://www.linkedin.com/in/simonegiannecchini ------------------------------------------------------- On Wed, Apr 1, 2009 at 11:38 AM, Christian Müller <[email protected]> wrote: > Ok, lets agree on that. For the preserving generalisation I use > the JTS TopologyPreservingSimplifier, how to do it for the non preserving > case ? > > > Andrea Aime writes: > >> Christian Müller ha scritto: >>> Looking at the the hint "Hints.PRESERVE_TOPOLOGY" indicates you mean the >>> generalization should take place in the FeatureSource ?. Would be >>> consistent with the handling of image pyramids. >> >> Well, in the feature source, yes, where else? You're asking the >> feature source to return pre-generalized geometries, where >> that does happen internally is an implementation detail. >> >> What I tried to say is that some generalization techniques do not >> preserve topology, they are usually faster than the topology >> preserving case: >> - for the rendering case we care more about performance and >> streaming renderer does not need topologically correct data anyways >> - for the wfs case we do want topology preservation instead, so >> it's ok to do more work >> >> I know that for your specific use case it does not make a difference, >> as you pre-generalize with a topology preserving algorithm, but what >> if tomorrow PostGIS comes out with a generalizing procedure that >> is geared towards rendering and performance and does not preserve >> topology, and we want to use it "on the fly" to get a speedup >> without the hassle of pre-generalizing, configuring and so on? >> I'm actually discussing this option with the PostGIS devs, I know >> for a fact people that would reject the complex setup of a pyramid >> but would be very happy to have a speedup in WMS rendering >> without the need to move a finger (as users). >> That's why I want to have around a topology preserving case, and >> a non topology preserving one, to support the on the fly, >> database side, generalization case. >> >> Cheers >> Andrea >> >> -- >> Andrea Aime >> OpenGeo - http://opengeo.org >> Expert service straight from the developers. > > > > ------------------------------------------------------------------------------ > _______________________________________________ > Geotools-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/geotools-devel > ------------------------------------------------------------------------------ _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
