AFAICS ST_ConcaveHull is written in PL/PgSQL, and doesn't use GEOS methods [1]. I suppose it is based on the common "alpha shapes" [1] approach. Martin has written something for JTS, but I think he hasn't release it yet...
giovanni [1] http://trac.osgeo.org/postgis/browser/trunk/postgis/postgis.sql.in.c#L4419 [2] http://www.mpi-inf.mpg.de/~jgiesen/tch/sem06/Celikik.pdf 2012/1/3 Andreas Neumann <a.neum...@carto.net> > Hi, > > Postgis SVN (2.0) has a function called ST_ConcaveHull ( > http://www.postgis.org/**documentation/manual-svn/ST_**ConcaveHull.html<http://www.postgis.org/documentation/manual-svn/ST_ConcaveHull.html>) > - it says it builds upon GEOS - (but probably only in geos-svn) - so there > should be some way to expose it in a future QGIS version. > > See also this thread: > http://www.mail-archive.com/**postgis-users@postgis.** > refractions.net/msg10785.html<http://www.mail-archive.com/postgis-users@postgis.refractions.net/msg10785.html> > > and Regina's examples: > http://www.bostongis.com/**postgis_concavehull.snippet<http://www.bostongis.com/postgis_concavehull.snippet> > > I currently can't find the GEOS class/method that calculates it, but since > Postgis makes a reference to GEOS it has to be somewhere in GEOS. > > If you want to speed up the process, you can perhaps pay a developer to > include it. > > Andreas > > On Tue, 3 Jan 2012 11:36:28 +0800, maning sambale wrote: > >> We have a nifty convex hull in ftools/vector plugin. I'm looking for >> ways to create concave hulls. I have a set of csv points as a source >> to generate the polygon. This is updated regularly by non-geo field >> workers. Any workaround to generate concave hull in QGIS? >> >> Mappy new year to all! >> >> PS. I've seen old discussions in the qgis-dev list. >> > > -- > -- > Andreas Neumann > Böschacherstrasse 10A > 8624 Grüt (Gossau ZH) > Switzerland > ______________________________**_________________ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/**mailman/listinfo/qgis-user<http://lists.osgeo.org/mailman/listinfo/qgis-user> >
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