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You might try adding a step to get the MultiPolygons from your Geometrycollection, see</div>
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<a href="https://postgis.net/docs/ST_CollectionExtract.html" id="OWA058ee274-5e3f-dc0f-a059-50521fa580d1" class="OWAAutoLink">https://postgis.net/docs/ST_CollectionExtract.html</a></div>
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Use type = 3 for polygons</div>
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UPDATE city_boundaries SET wayn3 = ST_Multi(ST_CollectionExtract(ST_Buffer(wayn2, -50, 'join=miter'),3));</div>
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Brent Wood<br>
<br>
Principal Technician, Fisheries<br>
NIWA<br>
DDI: +64 (4) 3860529</div>
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<div dir="ltr" id="divRplyFwdMsg" style="color: inherit;"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Luca Bertoncello <lucabert@lucabert.de><br>
<b>Sent:</b> Monday, December 23, 2024 03:40<br>
<b>To:</b> postgis-users@lists.osgeo.org <postgis-users@lists.osgeo.org><br>
<b>Subject:</b> Help with a query</span>
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<div style="font-size: 11pt;">Hi list!<br>
<br>
I have a query that worked some years with my "old" Debian 10 and<br>
Postgres 11.<br>
Now with Debian 12 and Postgres 15 throws an error...<br>
<br>
So, my problem: I need to create a table with the _physical_ boundaries<br>
of the cities.<br>
I already asked you some years ago and now I have my query.<br>
<br>
So I create a Table `city_boundaries`. Now I must "compact" it, in order<br>
to have only the outer polygon.<br>
The table has a column `way` defined as geometry(MultiPolygon,3857).<br>
<br>
As suggested 2021, I aggregate the building using 4 temporary columns,<br>
wayn1, wayn2, wayn3 and wayn4. They are defined too as<br>
geometry(MultiPolygon,3857).<br>
<br>
Then I run my queries:<br>
<br>
UPDATE city_boundaries SET wayn1 =<br>
ST_Multi(ST_SimplifyPreserveTopology(way, 100));<br>
UPDATE city_boundaries SET wayn2 = ST_Multi(ST_Buffer(wayn1, 50,<br>
'join=miter'));<br>
UPDATE city_boundaries SET wayn3 = ST_Multi(ST_Buffer(wayn2, -50,<br>
'join=miter'));<br>
UPDATE city_boundaries SET wayn4 = ST_Makevalid(wayn3);<br>
<br>
The last query throws the error:<br>
<br>
FEHLER: Geometry type (GeometryCollection) does not match column type<br>
(MultiPolygon)<br>
<br>
I suppose, in the last versions of PostGIS the Function ST_Makevalid<br>
will return something other than in the previous one.<br>
Can someone suggest me how to "convert" it as needed?<br>
<br>
Thanks a lot<br>
Luca Bertoncello<br>
(lucabert@lucabert.de)</div>
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<span>Brent Wood <br>
<font color="#1793d2">Principal Technician - GIS and Spatial Data Management</font><br>
<font color="#1793d2">Programme Leader - Environmental Information Delivery</font><br>
+64-4-386-0529<br>
<br>
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301 Evans Bay Parade Hataitai Wellington New Zealand<br>
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