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<p>Hi Werner</p>
<p>An old trick is to buffer using 0 units, which usually resolves self-intersections.</p>
<p>Cheers.</p>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">Regards,<br /><br />Nigel Berjak<br />Please consider the environment before printing this email.</div>
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<p id="reply-intro">On 2025-07-03 16:11, Isenmann, Werner (RPF) via QGIS-User wrote:</p>
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<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">Hi,</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">some colleagues have problems with shapefiles (really...) that contain polygons with self-intersections. The Vector Overlay - Clip tool, for example, cannot be executed because the algorithm does not run due to the self-intersection. Before executing the tool, the parameter ‘Invalid feature filtering’ can be set to ‘Skip (Ignore) Features with Invalid Geometies’. The faulty polygons are then skipped, which is not desirable, however.</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">QGIS offers various options for repairing self-intersections, for example:</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">1) Vector - Check Geometries plugin: however, this sometimes has very long runtimes which might not be acceptable.</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">2) Vector Geometry - Check Validity</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">a - Method QGIS: takes a very long time, or does not run through</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">b - Method GEOS: works correctly and quickly. However, only the first error is ever found. This is not convenient for files with many errors.</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">Does anyone know a good solution for repairing (many) self-intersections with high performance in QGIS?</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">Many thanks in advance,</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;">Werner</span></p>
<p class="v1MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><strong><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">---</span></strong></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><strong><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;"> </span></strong></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><strong><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">Werner Isenmann</span></strong></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;"> </span></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">Regierungspräsidium Freiburg</span></p>
<p class="v1MsoNormal" style="punctuation-wrap: simple; text-autospace: none;"><span style="font-size: 10.0pt; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">Referat 91 – Geowissenschaftliches Landesservicezentrum</span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif;"> </span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">Albertstraße 5</span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">D-79104 Freiburg i. Br.</span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif; mso-fareast-language: DE;"> </span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">Phone: (+49) 761 208-3008</span></p>
<p class="v1MsoNormal" style="line-height: 105%; text-autospace: ideograph-other;"><span style="font-size: 10.0pt; line-height: 105%; font-family: 'Arial',sans-serif; mso-fareast-language: DE;">E-Mail: <a href="mailto:Werner.Isenmann@rpf.bwl.de" rel="noreferrer"><span style="color: windowtext;">Werner.Isenmann@rpf.bwl.de</span></a></span></p>
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