[postgis-users] ST_Split with Multilinestring

[Birgit Laggner]

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
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/postgis-users
>
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