Help with a query

[Erik Wienhold]

On 2024-12-22 15:44 +0100, Luca Bertoncello wrote:
> > I suppose, in the last versions of PostGIS the Function ST_Makevalid
> > will return something other than in the previous one.
> 
> Some information more...
> 
> It seems, in some cases, the function ST_Makevalid returns
> ST_GeometryCollection instead of ST_MultiPolygon...
> Why?!?

See "dimensional collapse" on https://postgis.net/docs/ST_MakeValid.html

ST_MakeValid creates (multi)linestring and/or (multi)point geometries in
your case.  You can also try the structure algorithm with params
'method=structure keepcollapsed=false' and avoid ST_CollectionExtract.
But the linework and structure algorithms do not necessarily return the
same geometries, see the examples in the ST_MakeValid docs.

-- 
Erik Wienhold
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