Hi,
We published a document in early 2018 on geometry fixes.
This document should be revised, but may provide some elements.
(For example, geometry checker is now more stable under QGIS 3)
It is open for comments...
We have in our projects to produce a more user-friendly version
see :
http://geoinformations.metier.e2.rie.gouv.fr/spip.php?page=article&id_article=3522&id_rubrique=712
see the document at the bottom of the page
Regards,
Alain
FERRATON Alain
Ministère de la Transition écologique et solidaire (MTES)
SG/SPSSI/CPII/DOO
Chef du groupe Expertise Technique
02.40.12.84.08
Le 23/05/2019 à 13:07, > Richard McDonnell (par Internet, dépôt
[email protected]) a écrit :
Hi Finbar,
One other solution would be to use a double buffer, as in a positive buffer
something like 0.001, followed by a negative buffer of -0.001.
The issue you are facing is common, as most flood polygons are derived from
raster's and you can get a lot of self-intersections. The double buffer is in
my experience the handiest method of solving the issue. Also by using such a
small buffer, even a single buffer, will make little difference, to a house
being in or out of a flood zone, when taking into account the, resolutions of
the polygon datasets.
Hope this helps,
Regards,
Richard.
--
Richard McDonnell
GIS Specialist | FRM Data Management
Email: [email protected]
Phone: + 353 (0) 1 647 6543
Mobile: +353 (0) 87 688 5964
The Office of Public Works
52 St. Stephen's Green
Dublin 2 ~ D02 DR67
-----Original Message-----
From: Qgis-user <[email protected]> On Behalf Of GILLEN Finbar
Sent: 22 May 2019 11:40
To: [email protected]
Subject: Re: [Qgis-user] Fix Geometries
Thanks for all the responses on this... I am going to try the Check Validity
plugin ('QGIS' method) as a starter within QGIS 3.2. I am using a fairly
detailed flood polygon so accuracy is key. I will let you know how I get on.
Thanks again,
Finbar
-----Original Message-----
From: Qgis-user <[email protected]> On Behalf Of Nicolas Cadieux
Sent: 21 May 2019 23:02
To: [email protected]
Subject: Re: [Qgis-user] Fix Geometries
Hi,
The Geometry Checker plugin will add a the 'Check Geometries' option in the
vector menu. It is very unstable with the current version of QGIS. If you get
it to run, it should solve most problems. I get it to run when I only select
one test at a time.
The most predictable tool is the vector/geometry tools/Check validity using the
'QGIS' Method (not GEOS). That should fix your file. There is a 'remove
duplicate vertices' and 'delete duplicate geometries' in processing. Your
problem could also be caused by a module not working with multipart objects.
Go to vector/Geometry tools/Multiparts to singleparts.
If your lines don't touch, try the 'snap Geometries to layer ' in processing.
Nicolas
On 2019-05-21 2:54 a.m., Mithoefer wrote:
Hi Finnbar,
What plugin are you talking about and what QGIS version do you use?
You have a number of tools to check geometries. Try "Topology checker"
or "Geometry checker" to see where the problems are (invalid
geometries). Geometry checker is also able to fix some issues. Maybe
thats the one you use.
Anotehr option is GRASS GIS. Have you ever worked wit GRASS GIS? You
can create a GRASS database and import your polygons. GRASS GIS uses a
topolgical data model and is quite powerful in establishing a desent
data model with snapping options and clean functions. You can also try
GRASS tools from the processing framework like build polygons or clean.
Regards
Klaus
Am 20.05.19 um 11:31 schrieb GILLEN Finbar:
Hi All,
I have a few polygon layers where anytime I go to use them I have to
use the fix geometries plugin so that invalid geometries are fixed.
When I save the output from the fixed geometries plugin and add it in
a new project the same issues appears where I can’t use it accurately
to do a Select or Join by Location because some of the geometries are
still seen as invalid even though they have been ‘fixed’.
Is there anyway solution to this or do I have to keep using the fix
geometries plugin anytime I use the polygons for analysis?
Regards
Finbar
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