On 3/22/2013 1:53 PM, Hugues François wrote:
Hello,
Thanks for your answer Stephen. Of course dumping the multipolygons
works well with qgis. But for our users we need to keep the unique id
attached to each object, simple or multipolygon. They might need to
export data to their gis software for their work and all our database
is built based on this uniqueness constraint .
Well it is an attempt to work around a problem that is not related to
postgis. Another alternative might be to require your users to explode
multipolygons before getting to this point so the new records all have a
unique id.
In fact, I really don't understand why qgis see these as an error.
they seem topologically correct to me, especially since unioning the
dumped part in qgis create the same error ! Definitely, it sounds
like the error comes from qgis and the error seems impossible to
solve.
Right, if the bug is in qgis, then you can not expect postgis to fix it.
Sounds like you need to raise this as a bug on the qgis list and ask
them when you can expect a fix. For simplicity in conveying the problem
leave postgis out of it, as you can reproduce the problem without
postgis being involved.
-Steve W
Hugues.
-----Message d'origine----- De :
[email protected]
[mailto:[email protected]] De la part de Stephen
Woodbridge Envoyé : jeudi 21 mars 2013 22:11 À :
[email protected] Objet : Re: [postgis-users] The "bow
tie" error
On 3/21/2013 5:06 PM, Stephen Woodbridge wrote:
Francois,
Can you dump the polygons in the multiplyogon and create separate
records for them. So in you example graphic, you would end up with
two separate polygons the touch at a point. I think this would be
OK for qgis.
This might be helpful:
http://www.bostongis.com/postgis_dump.snippet
http://postgis.17.n6.nabble.com/converting-multipolygon-to-polygon-td3530291.html
-Steve W
On 3/21/2013 4:57 PM, Francois Hugues wrote:
Hello,
I have to deal with a dataset with a lot of errors. I ran a
st_makevalid which seems to give me good results (all polygons
then appear to be valid, closed and simple). But, when I open
this table as a layer in qgis it still throws me a lot of errors.
The image attached to this message provide you with an example
and the error said : Le segment 0 de l'anneau 16 du polygone 6
est intersecté au segment 0 de l'anneau 1 du polygone 7 à
933828.8196, 6261164.472 (in english this may be something like :
line 0 of ring 16 is intersected by line 0 of ring 1 of polygon 7
at point...).
As the rings of the multipolygon share one point, I tried to dump
it and then to union the rings to build a single polygon but I
got a multipolygon back and still an error.
The dataset have a lot of "bow ties" and it seems that
st_makevalid change them to multipolygon but that do not correct
all errors in qgis.
Does anyone have an idea to find any solution ?
Hugues
--
Hugues FRANÇOIS
[email protected]
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