---------- Forwarded message ---------- From: Matej Serc <mail...@tam.si> Date: 2011/7/22 Subject: Re: [Qgis-user] Table with empty wkb_geometry To: Andreas Neumann <a.neum...@carto.net>
Hello Andreas, you were right! There are some self-intersections in those parcels that are not returned correctly in intersections query. Is there any method to "correct" this issue as much automatically as possible? Thanks, Matej 2011/7/21 Andreas Neumann <a.neum...@carto.net> > Hi Matej, > > I would assume that the geometries are not empty to begin with. Some > software (like pgadmin) does not show you a WKB geometry if the geometry is > too big. But this does not mean that the geometry is empty. > > There are methods in Postgis to see if the geometry is empty: > http://postgis.refractions.**net/documentation/manual-1.5/** > ST_IsEmpty.html<http://postgis.refractions.net/documentation/manual-1.5/ST_IsEmpty.html> > > SELECT gid FROM your_schema.your_table WHERE ST_IsEmpty(the_geom); > > There is also a method to see if a geometry is valid (contains errors): > see http://postgis.refractions.**net/documentation/manual-1.5/** > ST_IsValidReason.html<http://postgis.refractions.net/documentation/manual-1.5/ST_IsValidReason.html> > > SELECT gid, ST_IsValidReason(the_geom) FROM your_schema.your_table WHERE > ST_IsValid(the_geom) = FALSE; > > Often, data imported from Shapefiles, contains errors, such as self > intersections, too few points, etc. - ST_IsValidReason() helps to find the > geometries. If you use the node tool in QGIS while in an editing session, > such errors are marked in green (no idea why they aren't marked in red - red > would be the color for errors in my opinion). > > Hope this helps. > > Andreas > > > On Thu, 21 Jul 2011 00:33:29 +0200, Matej Serc wrote: > >> Hi all, >> >> this is just partially connected with QGIS, but since I experience >> some behaviour which I can't understand, I will ask here. >> >> We have some parcel data which were imported to PostGIS DB from SHP >> files. I have just found out that there is a small percentage of the >> rows that have wkb_geometry field empty, but the parcel is visible in >> the QGIS, so I can click on it and Identify results etc. >> >> Basically I started looking at it more deeply when using some >> intersection functions from PostGIS that did not list some parcels >> which should by no means be listed. Now after looking at the SELECT >> query output in the pgAdmin, I see empty field for such parcels. >> >> What bothers me, is: how can these parcels be visible in QGIS? I think >> that there was some problem when I was importing the data from SHP - >> but no errors were shown in ogr2ogr at that time. Did anyone already >> experienced something like this? >> >> Thank you very much for any ideas and pointers in advance :-) >> BR, Matej >> > > -- > -- > 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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