[postgis-users] splitting linestrings with a polygon

[Nicolas Ribot]

Hi,

Keep the geometry column as multilinestring, as resulting splitting can
produce such objects, but add a st_multi after the intersection, on the
update clause:
... SET the_geom = st_multi(ST_Intersection(b.the_geom, p.the_geom))

It will force geometries to be multi, even if it only contains one object.
You can also extract the linear part of the intersection (as it can returns
point, line, or combination of both):
... SET the_geom =
st_multi(st_collectionExtract(ST_Intersection(b.the_geom, p.the_geom), 2))

Nicolas

On Tue, 20 Aug 2019 at 09:09, <paul.malm at lfv.se> wrote:

> Hi, I have a problem with MultiLinestrings/Linestrings.
>
> I have one layer with Linestrings which I would like to split in the
> intersections of a polygon (MultiPolygon) in a polygon layer.
>
>
>
> I tried this:
>
> UPDATE public."linelayer" b
>
>     SET the_geom = ST_Intersection(b.the_geom, p.the_geom)
>
>     FROM public."polygonlayer" p
>
>     WHERE ST_Intersects(b.the_geom, p.the_geom)
>
>
>
>
>
> I’m getting this error: ERROR: Geometry type (MultiLineString) does not
> match column type (LineString) SQL state: 22023
>
>
>
> Then I tried to make the Linsestrings to MultiLinestrings, before
> splitting the lines:
>
> ALTER TABLE public."linelayer" ALTER COLUMN "the_geom" TYPE
> geometry(MultiLinestring,"32633") USING ST_Multi("the_geom")
>
>
>
> And tried to split the lines again with the first expression, but gets
> this opposite error instead:
>
> ERROR: FEL: Geometry type (LineString) does not match column type
> (MultiLineString) SQL state: 22023
>
>
>
> What is it that I missed with MultiLinestring/Linestring?
>
>
>
> What the heck can I do, seems like “Moment 22”?
>
> Kind regards,
>
> Paul
>
>
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