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
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
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
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