Re: [Qgis-user] Micro-Geometry Problems
Steve (or any new QGIS users), For future reference, it is maybe better practice to digitise polygon sides simply as lines and then use one of the line>polygon tools in QGIS, GRASS or SAGA. Advantages are that you only digitise the lines once (much quicker, no double digitising) and so only require to use snapping at junctions (less change of snapping errors). Main disadvantage is that you would have to add your polygon attribute data after the polygons have been generated rather than as you digitise them. Regards, Mike GIS Cartographer University of Glasgow On 16/01/2020 14:48, Kirk Schmidt wrote: Hi All: This is a classic digitizing issue that can be corrected with GRAS as Harrisou suggests. If the layer does not get cleaned during the import process, you can use the grass functions v.build and v.clean to fix the digitizing slivers and incomplete intersections. Kirk Schmidt From: Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org] On Behalf Of DelazJ Sent: Wednesday, January 15, 2020 3:45 AM To: dhdeange...@comhem.se<mailto:dhdeange...@comhem.se> Cc: qgis-user Subject: Re: [Qgis-user] Micro-Geometry Problems Hi, There's also a "snap geometries to layer" Processing algorithm in QGIS that could be worth a look. https://docs.qgis.org/3.4/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#snap-geometries-to-layer Regards, Harrissou Le mer. 15 janv. 2020 à 08:34, Hernán De Angelis mailto:dhdeange...@comhem.se>> a écrit : Steve, In my opinion this is where GRASS topological vector model shines. One suggestion would be to import these vectors into a GRASS location and let GRASS clean the polygons and fix the topology automatically during import. My experience with similar problems is that after the import and cleaning there would be few if any errors of the sort you mention. In the worst case any surviving error is found it could in principle be solved by deleting the stubborn surface and digitizing it again. It will definitely not take two weeks of work! Good luck! H. On 2020-01-14 22:51, smiller...@cfl.rr.com<mailto:smiller...@cfl.rr.com> wrote: All- I have digitized a land use/land cover layer as individual polygons. The snap options were used and, for most vertices, the snap was precise. A vertex in polygon A has a precise match to a vertex in neighboring polygon B. But in 582 out of 2799 polygons, there are mis-matches in adjoining vertices that are only evident if you zoom into the layer at a magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent a couple of weeks trying to remedy these by hand using the Vertex Tool and other means. My question is this: is there an automated way in QIS to detect and remedy these situations? Thanks, Steve Miler ___ Qgis-user mailing list Qgis-user@lists.osgeo.org<mailto:Qgis-user@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org<mailto:Qgis-user@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org<mailto:Qgis-user@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Micro-Geometry Problems
Hi All: This is a classic digitizing issue that can be corrected with GRAS as Harrisou suggests. If the layer does not get cleaned during the import process, you can use the grass functions v.build and v.clean to fix the digitizing slivers and incomplete intersections. Kirk Schmidt From: Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org] On Behalf Of DelazJ Sent: Wednesday, January 15, 2020 3:45 AM To: dhdeange...@comhem.se Cc: qgis-user Subject: Re: [Qgis-user] Micro-Geometry Problems Hi, There's also a "snap geometries to layer" Processing algorithm in QGIS that could be worth a look. https://docs.qgis.org/3.4/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#snap-geometries-to-layer Regards, Harrissou Le mer. 15 janv. 2020 à 08:34, Hernán De Angelis a écrit : Steve, In my opinion this is where GRASS topological vector model shines. One suggestion would be to import these vectors into a GRASS location and let GRASS clean the polygons and fix the topology automatically during import. My experience with similar problems is that after the import and cleaning there would be few if any errors of the sort you mention. In the worst case any surviving error is found it could in principle be solved by deleting the stubborn surface and digitizing it again. It will definitely not take two weeks of work! Good luck! H. On 2020-01-14 22:51, smiller...@cfl.rr.com wrote: All- I have digitized a land use/land cover layer as individual polygons. The snap options were used and, for most vertices, the snap was precise. A vertex in polygon A has a precise match to a vertex in neighboring polygon B. But in 582 out of 2799 polygons, there are mis-matches in adjoining vertices that are only evident if you zoom into the layer at a magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent a couple of weeks trying to remedy these by hand using the Vertex Tool and other means. My question is this: is there an automated way in QIS to detect and remedy these situations? Thanks, Steve Miler ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Micro-Geometry Problems
About how to remedy these situations, you can use the v.clean GRASS provider algorithm, selecting the snap cleaning tool. Kind Regards, Gabriel El mié., 15 de ene. de 2020 a la(s) 16:10, Gabriel De Luca ( pablogabrieldel...@gmail.com) escribió: > When digitizing, coordinates are taken from the canvas and stored to the > layer. If the canvas (project) CRS is not the same as the layer CRS, a > transformation and/or conversion must be done between the taken and stored > coordinates. That transformation and/or conversion performed between the > previous vertex to be rendered, and the rendered coordinate digitized to be > stored, may lead a round trip error. > > If you are digitizing from a canvas CRS to the same layer CRS, and > snapping to vertex, I think that you will not see any difference between > both vertices. > > If you are snapping to intersections, you can see a difference also > working in the same CRS for the canvas and the layer, because an > intersection calculated coordinate may not be a rational number and at some > decimal place it must be truncated. > > I don't know if any rendering option could truncate the coordinate of a > vertex when rendering it, so when snapping to that vertex (in the same CRS > for the canvas and the layer) could return a truncated coordinate for the > digitized vertex. > > El mar., 14 de ene. de 2020 a la(s) 18:59, > escribió: > >> All- >> >> >> >> I have digitized a land use/land cover layer as individual polygons. The >> snap options were used and, for most vertices, the snap was precise. A >> vertex in polygon A has a precise match to a vertex in neighboring polygon >> B. >> >> >> >> But in 582 out of 2799 polygons, there are mis-matches in adjoining >> vertices that are only evident if you zoom into the layer at a >> magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent >> a couple of weeks trying to remedy these by hand using the Vertex Tool and >> other means. My question is this: is there an automated way in QIS to >> detect and remedy these situations? >> >> >> >> Thanks, >> >> Steve Miler >> ___ >> Qgis-user mailing list >> Qgis-user@lists.osgeo.org >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > > ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Micro-Geometry Problems
When digitizing, coordinates are taken from the canvas and stored to the layer. If the canvas (project) CRS is not the same as the layer CRS, a transformation and/or conversion must be done between the taken and stored coordinates. That transformation and/or conversion performed between the previous vertex to be rendered, and the rendered coordinate digitized to be stored, may lead a round trip error. If you are digitizing from a canvas CRS to the same layer CRS, and snapping to vertex, I think that you will not see any difference between both vertices. If you are snapping to intersections, you can see a difference also working in the same CRS for the canvas and the layer, because an intersection calculated coordinate may not be a rational number and at some decimal place it must be truncated. I don't know if any rendering option could truncate the coordinate of a vertex when rendering it, so when snapping to that vertex (in the same CRS for the canvas and the layer) could return a truncated coordinate for the digitized vertex. El mar., 14 de ene. de 2020 a la(s) 18:59, escribió: > All- > > > > I have digitized a land use/land cover layer as individual polygons. The > snap options were used and, for most vertices, the snap was precise. A > vertex in polygon A has a precise match to a vertex in neighboring polygon > B. > > > > But in 582 out of 2799 polygons, there are mis-matches in adjoining > vertices that are only evident if you zoom into the layer at a > magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent > a couple of weeks trying to remedy these by hand using the Vertex Tool and > other means. My question is this: is there an automated way in QIS to > detect and remedy these situations? > > > > Thanks, > > Steve Miler > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Micro-Geometry Problems
Hi, There's also a "snap geometries to layer" Processing algorithm in QGIS that could be worth a look. https://docs.qgis.org/3.4/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#snap-geometries-to-layer Regards, Harrissou Le mer. 15 janv. 2020 à 08:34, Hernán De Angelis a écrit : > Steve, > > In my opinion this is where GRASS topological vector model shines. One > suggestion would be to import these vectors into a GRASS location and let > GRASS clean the polygons and fix the topology automatically during import. > My experience with similar problems is that after the import and cleaning > there would be few if any errors of the sort you mention. In the worst case > any surviving error is found it could in principle be solved by deleting > the stubborn surface and digitizing it again. It will definitely not take > two weeks of work! > > Good luck! > > H. > > > On 2020-01-14 22:51, smiller...@cfl.rr.com wrote: > > All- > > > > I have digitized a land use/land cover layer as individual polygons. The > snap options were used and, for most vertices, the snap was precise. A > vertex in polygon A has a precise match to a vertex in neighboring polygon > B. > > > > But in 582 out of 2799 polygons, there are mis-matches in adjoining > vertices that are only evident if you zoom into the layer at a > magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent > a couple of weeks trying to remedy these by hand using the Vertex Tool and > other means. My question is this: is there an automated way in QIS to > detect and remedy these situations? > > > > Thanks, > > Steve Miler > > ___ > Qgis-user mailing listqgis-u...@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Micro-Geometry Problems
Steve, In my opinion this is where GRASS topological vector model shines. One suggestion would be to import these vectors into a GRASS location and let GRASS clean the polygons and fix the topology automatically during import. My experience with similar problems is that after the import and cleaning there would be few if any errors of the sort you mention. In the worst case any surviving error is found it could in principle be solved by deleting the stubborn surface and digitizing it again. It will definitely not take two weeks of work! Good luck! H. On 2020-01-14 22:51, smiller...@cfl.rr.com wrote: All- I have digitized a land use/land cover layer as individual polygons. The snap options were used and, for most vertices, the snap was precise. A vertex in polygon A has a precise match to a vertex in neighboring polygon B. But in 582 out of 2799 polygons, there are mis-matches in adjoining vertices that are only evident if you zoom into the layer at a magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent a couple of weeks trying to remedy these by hand using the Vertex Tool and other means. My question is this: is there an automated way in QIS to detect and remedy these situations? Thanks, Steve Miler ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
[Qgis-user] Micro-Geometry Problems
All- I have digitized a land use/land cover layer as individual polygons. The snap options were used and, for most vertices, the snap was precise. A vertex in polygon A has a precise match to a vertex in neighboring polygon B. But in 582 out of 2799 polygons, there are mis-matches in adjoining vertices that are only evident if you zoom into the layer at a magnification (i.e., a scale) of from 2:1 to 4 to 1. I have spent a couple of weeks trying to remedy these by hand using the Vertex Tool and other means. My question is this: is there an automated way in QIS to detect and remedy these situations? Thanks, Steve Miler ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
