[postgis-users] ST_Split with Multilinestring

Wed Jun 15 02:38:30 PDT 2016

Yes, this function will probably work - that's similar to what I meant 
with "looping the ST_Split with some function, DO block or pgScript 
after selecting all intersecting linestrings per polygon" in my original 
mail. If my current approach fails, too, I will revert to some sort of 
looping approach like the one you suggested. Thanks again for taking the 
time to analyze my problem!

Regards,

Birgit

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Dipl.-Geoökol. Birgit Laggner

Thünen-Institut für Ländliche Räume / Thünen Institute of Rural Studies
Bundesallee 50
38116 Braunschweig (Germany)

Tel: +49 531 596-5240
Mail: birgit.laggner at thuenen.de
Web: www.thuenen.de

Am 15.06.2016 um 11:27 schrieb Marcin Mionskowski:
> I think I finaly understand what you have and what you want to achieve 
> - take a look at polygon and multiline definitions :)
>
> If I'm right, this function should do the work:
>
> create table polygon
> (
> id serial,
> geom geometry,
> done smallint default 0
> );
> create table multiline
> (
> id serial,
> geom geometry,
> done smallint default 0
> );
> create table line
> (
> id serial,
> geom geometry,
> done smallint default 0
> );
>
> insert into polygon (geom)
> select ST_Buffer(ST_GeomFromText('POINT(10 10)'), 10);
>
> insert into multiline (geom)
> select ST_Union(
>     (select ST_MakeLine(ST_MakePoint(0, 1),ST_MakePoint(20, 21))),
>     (select ST_MakeLine(ST_MakePoint(1, 0),ST_MakePoint(20, 19)))
>     );
>
> create or replace function test() returns void as
> $BODY$
>
>     declare ln geometry;
>         i int;
>
> BEGIN
>     truncate table line;
>
>     insert into line (geom)
>     select (ST_Dump(geom)).geom
>     from multiline;
>
>     loop
>         select geom,id
>         into ln,i
>         from line
>         where done=0
>         limit 1;
>
>         with
>         del as (
>             delete from polygon p
>             where ST_Intersects(p.geom,ln)
>             returning p.geom
>             )
>         insert into polygon (geom)
>         select (st_dump(st_split(del.geom,ln))).geom
>         from del;
>
>         update line
>         set done=1
>         where id=i;
>
>         exit when i is null;
>     end loop;
> end;
> $BODY$
> LANGUAGE plpgsql;
>
> select test();
>
>
>
> On Wed, 15 Jun 2016 11:10:33 +0200, Birgit Laggner 
> <birgit.laggner at thuenen.de> wrote:
>
>> Dear list,
>>
>> @Marcone: Unfortunately, the st_multi didn't change anything. The error
>> message is still the same.
>>
>> Next, I will try some function from a user example from 2008
>> (https://trac.osgeo.org/postgis/wiki/UsersWikiSplitPolygonWithLineString). 
>>
>> Maybe this will be a workaround.
>>
>> But I am still wondering why I get the error message at all. I did find
>> a PostGIS ticket addressing the same functionality
>> (https://trac.osgeo.org/postgis/ticket/3097) and there is mentioned that
>> the problem is fixed with PostGIS 2.2.0. My PostGIS version is
>> "POSTGIS="2.2.1 r14555" GEOS="3.5.0-CAPI-1.9.0 r4084" PROJ="Rel. 4.9.1,
>> 04 March 2015" GDAL="GDAL 1.11.2, released 2015/02/10" LIBXML="2.9.2"
>> LIBJSON="0.11.99" TOPOLOGY RASTER". So, I would suppose I shouldn't have
>> this problem.
>>
>> Any other ideas?
>>
>> Thanks and regards,
>>
>> Birgit
>>
>> Am 15.06.2016 um 10:01 schrieb Birgit Laggner:
>>> Hi Marcin,
>>>
>>> thanks for your reply. I don't think, that will provide the results I
>>> am looking for. I am deliberately aggregating all intersecting lines
>>> with ST_Union because otherwise the query would result in several
>>> collections per polygon, each collection containig the st_split result
>>> for one of the intersecting lines (blades). But I want the polygon cut
>>> with all blades.
>>>
>>> Currently I am trying Marcone's suggestion (although I cannot imagine
>>> why this should solve anything - but you never know until you try,
>>> right?).
>>>
>>> So, thank you both, Marcin and Marcone!
>>>
>>> Regards,
>>>
>>> Birgit
>>>
>>> Am 15.06.2016 um 09:24 schrieb Marcin Mionskowski:
>>>> On Tue, 14 Jun 2016 15:37:40 +0200, Marcone <marconeperes at gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>> 2016-06-14 9:52 GMT-03:00 Birgit Laggner <birgit.laggner at thuenen.de>:
>>>>>> I would like to use the ST_Split function to split polygons from one
>>>>>>    table with all intersecting lines from another table.
>>>>>> Unfortunately,
>>>>>>    I get the following error:
>>>>>>
>>>>>>      ERROR: Splitting a Polygon by a MultiLineString is unsupported
>>>>>>
>>>>>>    SQL Status:XX000
>>>>>>
>>>>>>      This is my query:
>>>>>>
>>>>>>      select betr_id, (cut).path[1], (cut).geom from (select betr_id,
>>>>>>    st_dump(st_split) as cut from (select a.betr_id, ST_Split(a.geom,
>>>>>>    st_union(b.geom)) from p_sam.nihb_2013_convex_hull_betr a left 
>>>>>> join
>>>>>>    p_sam.ni_dlm13_aaa_gew_sie_ver_l b on st_intersects(a.geom, 
>>>>>> b.geom)
>>>>>>    group by a.betr_id, a.geom) sel1) sel2;
>>>>>>
>>>>>>      The Manual contains the following info regarding this problem:
>>>>>>
>>>>>>      "The function supports splitting a line by (multi)point,
>>>>>> (multi)line
>>>>>>    or (multi)polygon boundary, a (multi)polygon by line."
>>>>>>
>>>>>>      This might mean that I would be able to split a line by
>>>>>>    multilinestrings, but a polygon only by single linestrings - is
>>>>>> that
>>>>>>    correct? Does anyone has a suggestion how I could work around 
>>>>>> this
>>>>>>    problem (aside from looping the ST_Split with some function, DO
>>>>>>    block or pgScript after selecting all intersecting linestrings 
>>>>>> per
>>>>>>    polygon)?
>>>>>>
>>>>>>      Thanks a lot for any helpful suggestions!
>>>>>
>>>>> I'm not sure if I understand your problem, but try use
>>>>> ST_Split(st_multi(a.geom),
>>>>>    st_union(b.geom)). I'm not test this, but I think that will solve
>>>>> your problem.
>>>>>
>>>>> Best regards.
>>>>>
>>>>>
>>>>>
>>>> Have you tried to ST_Dump multilinestrings first?
>>>> Using CTE this could look like:
>>>>
>>>> with
>>>> a as ( --polygon
>>>>     select ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) a
>>>>     ),
>>>> b as ( --multilinestring
>>>>     select ST_Union(
>>>>         (select ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190,
>>>> 190))),
>>>>         (select ST_MakeLine(ST_MakePoint(191, 191),ST_MakePoint(200,
>>>> 200)))
>>>>     ) b
>>>>     ),
>>>> c as ( --multilinestring dump -> 2 separate linestrings
>>>>     select (ST_Dump(b)).geom c
>>>>     from b
>>>>     )
>>>>
>>>> SELECT ST_AsText(ST_Split(a, c))
>>>> from a,c
>>>> where ST_Intersects(a,c)
>>>>
>>>> Intersection check is done here on line parts.
>>>>
>>>> Regards
>>>> _______________________________________________
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>>>> postgis-users at lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/postgis-users
>>>
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