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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Just a quick one, you could try the
<b>Topology Checker<o:p></o:p></b></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><a href="https://docs.qgis.org/2.8/en/docs/user_manual/plugins/plugins_topology_checker.html">https://docs.qgis.org/2.8/en/docs/user_manual/plugins/plugins_topology_checker.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">This should help you locate things like Self Intersections. You will have to manually fix the error, but at least you have a way to
find the issues.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Regard’s,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Richard.<o:p></o:p></span></p>
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——</span><br>
<span style="FONT-FAMILY: Arial, sans-serif; FONT-WEIGHT: bold; COLOR: #004d44">Richard McDonnell MSc GIS, FME Certified Professional</span><br>
<span style="FONT-FAMILY: Arial, sans-serif; COLOR: #004d44"><i>FRM Data Management</i></span><br>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Qgis-user <qgis-user-bounces@lists.osgeo.org>
<b>On Behalf Of </b>Alister Hood<br>
<b>Sent:</b> 01 June 2021 23:06<br>
<b>To:</b> qgis-user@lists.osgeo.org<br>
<b>Subject:</b> Re: [Qgis-user] Is this a bug in the vector clipping algorithm?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">OK, I thought I had tried "Check validity" with both QGIS and GEOS methods, but I must have got confused and only used GEOS method, which doesn't detect an error.<o:p></o:p></p>
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<p class="MsoNormal">The first tool I tried was actually "Fix geometries", which also thinks the geometries are valid. Maybe fix geometries uses GEOS and needs to be enhanced with a QGIS method. <o:p></o:p></p>
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<p class="MsoNormal">It seems strange for other algorithms like "clip" to do more fixing than "fix geometries", especially in a case like this where you would think the feature could be clipped without any "fixing".<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Date: Tue, 1 Jun 2021 02:45:51 -0700 (MST)<br>
From: Andrea Giudiceandrea <<a href="mailto:andreaerdna@libero.it" target="_blank">andreaerdna@libero.it</a>><br>
To: <a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</a><br>
Subject: Re: [Qgis-user] Is this a bug in the vector clipping<br>
algorithm?<br>
Message-ID: <<a href="mailto:1622540751842-0.post@n6.nabble.com" target="_blank">1622540751842-0.post@n6.nabble.com</a>><br>
Content-Type: text/plain; charset=us-ascii<br>
<br>
Alister Hood-2 wrote<br>
> I haven't been able to find a tool for validating or repairing geometries<br>
> that thinks there is a problem with the original geometry<br>
<br>
Hi Alister,<br>
what tool have you used to check the geometry?<br>
<br>
Have you tried to use the Geometry Checker core plugin (Vectror->Check<br>
Geometries) or the "Check validity" (qgis:checkvalidity) processing tool<br>
(with the QGIS method)?<br>
They both report errors: "duplicate node", "self contact", "duplicate<br>
nodes".<br>
<br>
Also the ArcMap/ArcGIS Check Geometry tool reports "self intersections".<br>
<br>
Anyway it seem the QGIS Clip tool does a "sanitize" of the intersection<br>
result (always converting to Multi Type).<br>
<br>
Regards.<br>
<br>
Andrea Giudiceandrea<o:p></o:p></p>
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