Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
On 01/19/2014 07:09 AM, Richard Duivenvoorde wrote: On 15-01-14 19:28, Lynkos wrote: Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. Hi Sarah, I was curious what was happening here, and was questioning if it was a QGIS fault, or a GEOS (the underlying lib which takes care of the merging) one. I loaded your shape in Postgis as table 'merge', and merged those geoms via: insert into merge (id_0, id, geom) VALUES (999, 999, (select ST_Multi(ST_UNION (geom)) from merge where id_0 in (24,25,29)) ) but this looked exactly the same as your merged shape... (postgis also uses GEOS :-) )... So the problem is indeed: http://lists.osgeo.org/pipermail/qgis-developer/2014-January/030119.html looking into the docs of geos, there was talking about a buffer. Which made me think about: what about adding (and later removing a small buffer). So just before the merge, add a small buffer (1): insert into merge (id_0, id, geom) VALUES (999, 999, (select ST_Multi(ST_UNION (st_buffer(geom,1))) from merge where id_0 in (24,25,29)) ) which then did NOT sow the artifacts anymore, but indeed is one meter too big. So now a negative buffer (-1) over that one: insert into merge (id_0, id, geom) VALUES (, , (select ST_Multi(st_buffer(geom,-1)) from merge where id_0 = 999)) And I think you have what you want... http://www.flickr.com/photos/97361298@N07/12031619434/ http://www.flickr.com/photos/97361298@N07/12031256205/ Off course this can give other artifacts sometimes (because you are actually merging the buffered geometries), but I think it is better then a normal merge... It's pretty easy to do this in postgis, but can probably also been done via processing? Regards, Richard I can't see any of the original images or files posted of the issue, but I assume this is topology related. Especially if the buffer solves it. Other ways to get there: v.clean in the GRASS part of the Processing toolbox, choose advanced and set a tolerance - it's similar to the buffer procedure. Looking at Richard's output my guess is you need to start thinking about using the topology tools either in QGIS, Postgis or GRASS. Being a valid geometry and being topology valid are 2 different things (topology does not allow overlap, overlapping regions become a 3rd region of joint value). Thanks, Alex ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
On 15-01-14 19:28, Lynkos wrote: Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. Hi Sarah, I was curious what was happening here, and was questioning if it was a QGIS fault, or a GEOS (the underlying lib which takes care of the merging) one. I loaded your shape in Postgis as table 'merge', and merged those geoms via: insert into merge (id_0, id, geom) VALUES (999, 999, (select ST_Multi(ST_UNION (geom)) from merge where id_0 in (24,25,29)) ) but this looked exactly the same as your merged shape... (postgis also uses GEOS :-) )... So the problem is indeed: http://lists.osgeo.org/pipermail/qgis-developer/2014-January/030119.html looking into the docs of geos, there was talking about a buffer. Which made me think about: what about adding (and later removing a small buffer). So just before the merge, add a small buffer (1): insert into merge (id_0, id, geom) VALUES (999, 999, (select ST_Multi(ST_UNION (st_buffer(geom,1))) from merge where id_0 in (24,25,29)) ) which then did NOT sow the artifacts anymore, but indeed is one meter too big. So now a negative buffer (-1) over that one: insert into merge (id_0, id, geom) VALUES (, , (select ST_Multi(st_buffer(geom,-1)) from merge where id_0 = 999)) And I think you have what you want... http://www.flickr.com/photos/97361298@N07/12031619434/ http://www.flickr.com/photos/97361298@N07/12031256205/ Off course this can give other artifacts sometimes (because you are actually merging the buffered geometries), but I think it is better then a normal merge... It's pretty easy to do this in postgis, but can probably also been done via processing? Regards, Richard ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
Thanks to everyone for the help and suggestions so far. I've uploaded all the shapefile parts here (sorry, yesterday I was in a rush and I just wasn't thinking): https://www.dropbox.com/s/ru4s3bi2bt5z4c2/QGIS-merge.zip This file is the result of several save-as operations, so the problem outlined by Paolo could be a factor. But I've also tried with the original shape file (which should be as drawn) and it behaves in exactly the same way. Thanks again, Sarah. 2014/1/16 Tim Sutton li...@linfiniti.com HI Sarah Can you post all the parts of the shapefile that others may test (.shp alone is not enough we need .dbf and .shx too). Regards Tim ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
[Qgis-user] Fwd: Merging polygons leaves isolated lines
I've been given a shape file representing a vegetation map which I now have to modify, merging a number of polygons. When I do this, in almost all cases the merge leaves a number of lines, either attached to one of the polygons or completely isolated. An example of the problem (one of the worst) is illustrated in the following screenshots. Firstly a section of the shape: https://www.dropbox.com/s/amik6g9cdoqg84b/Screenshot%202014-01-15%2017.42.18.jpg The three polygons to be merged selected: https://www.dropbox.com/s/6gl83y2jwgxvrje/Screenshot%202014-01-15%2017.42.33.jpg The section of the shape after the merge: https://www.dropbox.com/s/f1iem85kidkwkwx/Screenshot%202014-01-15%2017.42.53.jpg And a close-up of the unattached lines left after the operation: https://www.dropbox.com/s/i4rmyi7apcfpgg9/Screenshot%202014-01-15%2017.44.05.jpg In case it is relevant, here are my snap options: https://www.dropbox.com/s/73ky3qgbzk16esj/Screenshot%202014-01-15%2017.44.30.jpg And here is a part of the shape file: https://www.dropbox.com/s/n2asd9urvyd5fc8/merge-test.shp If I had just a few polygons to merge, I could simply eliminate the lines, but the file contains about 500, a large proportion of which must be merged. I imagine the problem is caused by errors in the original polygons, but the errors don't show up on either visual examination or using the verify validity function. Any ideas on what the problem might be and how to resolve it, if possible, eliminating it at the roots by correcting the original shape? Thanks, Sarah. P.S. Let me know if you have problems visualizing the images or downloading the file. -- *Sarah Gregg* ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Il 15/01/2014 18:17, Lynkos ha scritto: I've been given a shape file representing a vegetation map which I now have to modify, merging a number of polygons. When I do this, in almost all cases the merge leaves a number of lines, either attached to one of the polygons or completely isolated. An example of the problem (one of the worst) is illustrated in the following screenshots. Hi Lynkos, I think this is another side of this issue: http://lists.osgeo.org/pipermail/qgis-developer/2014-January/030119.html Contributions welcome. All the best. - -- Paolo Cavallini - www.faunalia.eu Corsi QGIS e PostGIS: http://www.faunalia.eu/training.html -BEGIN PGP SIGNATURE- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlLWzVIACgkQ/NedwLUzIr5FfACfQ8GfFPlfFw+gCN5Qnb5609wR s7sAn3iGkHiGWCZlEoLxE+5f7/5GgY4q =qUQR -END PGP SIGNATURE- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. 2014/1/15 Paolo Cavallini cavall...@faunalia.it -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Il 15/01/2014 18:17, Lynkos ha scritto: I've been given a shape file representing a vegetation map which I now have to modify, merging a number of polygons. When I do this, in almost all cases the merge leaves a number of lines, either attached to one of the polygons or completely isolated. An example of the problem (one of the worst) is illustrated in the following screenshots. Hi Lynkos, I think this is another side of this issue: http://lists.osgeo.org/pipermail/qgis-developer/2014-January/030119.html Contributions welcome. All the best. - -- Paolo Cavallini - www.faunalia.eu Corsi QGIS e PostGIS: http://www.faunalia.eu/training.html -BEGIN PGP SIGNATURE- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlLWzVIACgkQ/NedwLUzIr5FfACfQ8GfFPlfFw+gCN5Qnb5609wR s7sAn3iGkHiGWCZlEoLxE+5f7/5GgY4q =qUQR -END PGP SIGNATURE- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- *Sarah Gregg* immagini - parole - territorio - natura Web: www.wild-eyes.eu ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
On 15-01-14 19:28, Lynkos wrote: Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. Hi All, People from the Technical University Delft have created an automated way for: Validation and Automatic Repair of Planar Partitions. It is called 'pprepair'. I'm not 100% sure it fixes your problem, but as a commandline tool it is pretty easy to run. It's pure c++ but has cgal as dependency. On debian it was 2 minutes to build and run. Code is here: https://github.com/tudelft-gist/pprepair Some theory: http://www.gdmc.nl/ken/files/12_osgis.pdf And Barry blogging about it: http://geospaced.blogspot.nl/2012/09/fixing-polygons-with-pprepair.html If interesting, have it a go. Regards, Richard Duivenvoorde ps actually I promised the TU people to write a simple qgis plugin for calling it in a separate process (like we do with gdal commands), so if you are on it. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
Il 15/01/2014 21:06, Richard Duivenvoorde ha scritto: On 15-01-14 19:28, Lynkos wrote: Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. Hi All, People from the Technical University Delft have created an automated way for: Validation and Automatic Repair of Planar Partitions. It is called 'pprepair'. I'm not 100% sure it fixes your problem, but as a commandline tool it is pretty easy to run. It's pure c++ but has cgal as dependency. On debian it was 2 minutes to build and run. Code is here: https://github.com/tudelft-gist/pprepair Some theory: http://www.gdmc.nl/ken/files/12_osgis.pdf And Barry blogging about it: http://geospaced.blogspot.nl/2012/09/fixing-polygons-with-pprepair.html If interesting, have it a go. Regards, Richard Duivenvoorde ps actually I promised the TU people to write a simple qgis plugin for calling it in a separate process (like we do with gdal commands), so if you are on it. good stuff! a Processing provider would be much welcome. The availability of packages for many platforms will be the limiting factor for its spread, however. Do you know if the authors have plans to package it for e.g. Debian and OSGeo4W? Thanks. -- Paolo Cavallini - www.faunalia.eu QGIS PostGIS courses: http://www.faunalia.eu/training.html ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Fwd: Merging polygons leaves isolated lines
HI Sarah Can you post all the parts of the shapefile that others may test (.shp alone is not enough we need .dbf and .shx too). Regards Tim On Wed, Jan 15, 2014 at 8:28 PM, Lynkos lynkosm...@gmail.com wrote: Thanks Paolo for the rapid response. It does look as though my problem is related. Any guidance on how I can clean up the original shapefile? Sarah. 2014/1/15 Paolo Cavallini cavall...@faunalia.it -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Il 15/01/2014 18:17, Lynkos ha scritto: I've been given a shape file representing a vegetation map which I now have to modify, merging a number of polygons. When I do this, in almost all cases the merge leaves a number of lines, either attached to one of the polygons or completely isolated. An example of the problem (one of the worst) is illustrated in the following screenshots. Hi Lynkos, I think this is another side of this issue: http://lists.osgeo.org/pipermail/qgis-developer/2014-January/030119.html Contributions welcome. All the best. - -- Paolo Cavallini - www.faunalia.eu Corsi QGIS e PostGIS: http://www.faunalia.eu/training.html -BEGIN PGP SIGNATURE- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlLWzVIACgkQ/NedwLUzIr5FfACfQ8GfFPlfFw+gCN5Qnb5609wR s7sAn3iGkHiGWCZlEoLxE+5f7/5GgY4q =qUQR -END PGP SIGNATURE- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- *Sarah Gregg* immagini - parole - territorio - natura Web: www.wild-eyes.eu ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- Tim Sutton - QGIS Project Steering Committee Member == Please do not email me off-list with technical support questions. Using the lists will gain more exposure for your issues and the knowledge surrounding your issue will be shared with all. Irc: timlinux on #qgis at freenode.net == ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
