[postgis-users] breake lines

[paul.malm at lfv.se]

Hi,
If I understand your question correct, yes I would like to break all lines in the intersections with another layer.
No I have not tried MultiLinestrings comprised of all lines that are intersecting the lines to be broken. Don’t know how to do this. ☹

This is how far I have come:

CREATE TABLE splittedlayer3
AS SELECT ST_CollectionExtract(ST_Split(o.the_geom, c.the_geom),2) as the_geom
FROM "orgLayer" o, "cutLayer" c WHERE ST_Intersects(o.the_geom, c.the_geom)

But this gives duplicate line segments when intersecting the cutting lines twice.
/Paul

Från: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] För Martin Davis
Skickat: den 3 september 2019 19:18
Till: PostGIS Users Discussion
Ämne: Re: [postgis-users] breake lines

Have you tried using ST_Split passing each input line and for the second argument a MultiLineString comprised of all lines that it might intersect (obtained via BBOX or ST_Intersects query)?  It seems like that should not create any duplicate linework from the input line.

As far as I know there's no other way to do this using current PostGIS functions.   It's an interesting requirement - it sounds like essentially you want to node one layer against another.  There's actually the machinery to do this internally in PostGIS/GEOS, but it's never come up as a requirement before, so has not been exposed as a function.

What is your use case?

On Tue, Sep 3, 2019 at 9:48 AM <paul.malm at lfv.se<mailto:paul.malm at lfv.se>> wrote:
If I split lines with another line layer, I will get a lot of duplicaded line segments since the lines could be intersected several times. It is not possible to use update on the table when splitting one geomety to two.
I think it must be possible, but I’m not that skilled in SQL and I’ve not found any examples on the net.

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