Re: [Qgis-user] concave hull/alpha shapes in QGIS
Thanks for the tips Alex, Andreas and Giovanni. Unfortunately, I need to turnover the maintenance of the data to a non-geo user, hence I need a workflow that can avoid R or postgis for now. On Tue, Jan 3, 2012 at 6:13 PM, G. Allegri gioha...@gmail.com wrote: 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) - 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 and Regina's examples: 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 ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- cheers, maning -- Freedom is still the most radical idea of all -N.Branden wiki: http://esambale.wikispaces.com/ blog: http://epsg4253.wordpress.com/ -- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] concave hull/alpha shapes in QGIS
On 01/02/2012 07:36 PM, 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. They can be done in R, and therefore done using ManageR QGIS plugin. The R package is alphahull Though you might want to look at other methods depending on what your actual goal. I messed around with them in regards to territories from GPS telemetry and I believe Anne Ghisla has a whole thesis on the topic. In the end a professor of mine came up with using a density function as the fastest method to get good results. I can find the R code if it will help you. Thanks, Alex ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] concave hull/alpha shapes in QGIS
Hi, Postgis SVN (2.0) has a function called ST_ConcaveHull (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 and Regina's examples: 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
Re: [Qgis-user] concave hull/alpha shapes in QGIS
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.htmlhttp://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.htmlhttp://www.mail-archive.com/postgis-users@postgis.refractions.net/msg10785.html and Regina's examples: http://www.bostongis.com/**postgis_concavehull.snippethttp://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-userhttp://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
[Qgis-user] concave hull/alpha shapes in QGIS
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. -- cheers, maning -- Freedom is still the most radical idea of all -N.Branden wiki: http://esambale.wikispaces.com/ blog: http://epsg4253.wordpress.com/ -- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
