'Re: [Qgis-user] Request help 'Aggregate polygons' QGIS 3'

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List:       qgis-user
Subject:    Re: [Qgis-user] Request help 'Aggregate polygons' QGIS 3
From:       FT <flavio.taccaliti () libero ! it>
Date:       2019-11-26 16:39:47
Message-ID: 16386cfa-475f-40de-a469-0192f741b56d () email ! android ! com
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<div dir='auto'>Dear Andy,<div dir="auto"><br></div><div dir="auto">Thank you very \
much for your help, I will try the procedure immediately.</div><div dir="auto">You \
definitely gave me a hand.</div><div dir="auto"><br></div><div dir="auto">All the \
best,</div><div dir="auto"><br></div><div dir="auto">Flavio</div></div><div \
class="gmail_extra"><br><div class="gmail_quote">Il 25 nov 2019 17:32, &quot;Harfoot \
A.J.&quot; &lt;ajph@geodata.soton.ac.uk&gt; ha scritto:<br type="attribution" \
/><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"><div> <p>Hi Flavio,</p>
<p>I&#39;m not aware of a single tool that is the exact equivalent of the ArcGIS \
one.</p> <p>The Concave hull (k-nearest neighbor) tool (part of the QGIS Processing \
toolbox, not a plugin) will generate the the bounding polygon, but does not allow \
input data to be grouped by a separation distance, but will accept a &#39;group&#39; \
field which creates a polygon  for each set of features having the same value for the \
field. This allows the separation distance to be incorporated:</p> <ol><li>Buffer the \
polygons by the maximum separation distance required, dissolving the \
results</li><li>Spatially join the original polygons to the buffer output so that \
each original polygon receives the unique id of the buffer polygon that it falls \
within</li><li>Create concave hulls using the buffer id field as the group \
field.</li></ol> <p>This sequence could be easily added to a model, simplifying and \
reducing the chances of errors when executing.<br /> </p>
<p>Andy</p>
<p><br />
</p>
<div>On 21/11/2019 17:46, <a href="mailto:flavio.taccaliti&#64;libero.it">
flavio.taccaliti&#64;libero.it</a> wrote:<br />
</div>
<blockquote>
<div>Hi everyone, </div>
<div><br />
</div>
<div>This is my first message in a users&#39; group, I hope not to break any \
&#34;netiquette&#34; rule. </div>
<div><br />
</div>
<div>I have come across this little problem, and I would like to ask you if there is \
a simple solution to it: <br />
I am looking for a QGIS 3 tool similar to ArcGIS &#34;Aggregate polygons&#34;, <a \
href="http://desktop.arcgis.com/en/arcmap/10.3/tools/cartography-toolbox/aggregate-polygons.htm">
 http://desktop.arcgis.com/en/arcmap/10.3/tools/cartography-toolbox/aggregate-polygons.htm</a> \
( (it takes a multipolygon layer and aggregate the polygons that are closer than a \
given distance). </div>
<div><br />
</div>
<div>I have come across some results on the web, like using PostGIS (<a \
href="https://gis.stackexchange.com/questions/113084/qgis-equivalent-to-arcgis-aggrega \
te-polygons">https://gis.stackexchange.com/questions/113084/qgis-equivalent-to-arcgis-aggregate-polygons</a>)
  or <br />
Unfortunately, I have no experience with Postgres or SQL yet, and given the limited \
amount of time I have for this task it would be unfeasible for me to learn them now. \
</div> <div><br />
</div>
<div>&#34;Concave hull&#34; tool (<a \
href="https://plugins.qgis.org/plugins/concavehull/">https://plugins.qgis.org/plugins/concavehull/</a>) \
does not what I am looking for, as I would like to set the maximum distance between \
polygons in  the clusters, not the maximum number of polygons. <br />
Also &#34;aggregate&#34; function seems to me not to aggregate polygons by their \
proximity (<a href="https://docs.qgis.org/testing/en/docs/user_manual/processing_algs/ \
qgis/vectorgeometry.html#aggregate">https://docs.qgis.org/testing/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#aggregate</a>).
 </div>
<div><br />
</div>
<div>For the moment I have used the ArcGIS tool on another computer, but the idea is \
to write down some simple instructions for other users who will have even less \
expertise than me. Maybe the &#34;button&#34; already exists in QGIS 3, in that case \
excuse me for the  repetition. </div>
<div><br />
</div>
<div>Thank you in advance for any suggestion or indication. </div>
<div><br />
</div>
<div>Best regards, </div>
<div><br />
</div>
<div>FT </div>
<br />
<fieldset></fieldset>
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 </blockquote>
<pre>-- 
Andy Harfoot

GeoData Institute
University of Southampton
Southampton
SO17 1BJ

Tel:  &#43;44 (0)23 8059 2719

<a href="http://www.geodata.soton.ac.uk">www.geodata.soton.ac.uk</a></pre>
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