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<p>(not tested !!)<br>
</p>
<p>UPDATE a_table AS a SET a.geom = b.cgeom from (select name,
ST_ConcaveHull(ST_Collect(geom), 0.99) as cgeom from b_table group
by name having count(*) >= 3) AS b WHERE a.name = b.name </p>
<div class="moz-cite-prefix">the "count(*) >= 3" removes point
collections which will result in degenerative concave hulls</div>
<div class="moz-cite-prefix"> <br>
</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">Den 27-04-2020 kl. 12:29 skrev
Shaozhong SHI:<br>
</div>
<blockquote type="cite"
cite="mid:CA+i5JwbR+dzO0-DHL4DpYggj81rwiHtz4Sxvuv-dOtARa5bvUQ@mail.gmail.com">
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<div dir="ltr">I added a new column.
<div><br>
</div>
<div>alter table a_table add column geom geometry(Polygon,
27700);<br>
</div>
<div><br>
</div>
<div>Then, </div>
<div><br>
</div>
<div>update a_table set geom = (select
ST_ConcaveHull(ST_Collect(geom), 0.99) from b_table where name
= _name) where name = _name;<br>
</div>
<div><br>
</div>
<div>It kept throwing up an error message saying: "geometry type
point does not match polygon".</div>
<div><br>
</div>
<div>I thought that a concavehyll is a polygon. That is why I
created a polygon column for it.</div>
<div><br>
</div>
<div>Can anyone help?</div>
<div><br>
</div>
<div>Regards,</div>
<div><br>
</div>
<div>Shao</div>
</div>
<br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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<pre class="moz-signature" cols="72">--
Med venlig hilsen / Kind regards
Bo Victor Thomsen
</pre>
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