[postgis-users] splitting a linestring with points

[Olivier Leprêtre]

Thanks Marcin, that was the point, doing a st_union with the set of points generates cuts along the line.

Thanks also to Martin, Nicolas, Alexandre for your precious help and suggestions.

Nice week-end to all of you,

Olivier

-----Message d'origine-----
De : Marcin Mionskowski [mailto:mionskowskimarcin at gmail.com] 
Envoyé : vendredi 9 février 2018 14:05
À : 'PostGIS Users Discussion'; Olivier Leprêtre
Objet : Re: [postgis-users] splitting a linestring with points

When you split one linestring with one point you will get as a result two linestrings, thats why your result will be a GEOMETRYCOLLECTION. You can than "explode" it with st_dump.


Try the example below (one line and teo points "spliting" it -> 3 linestrings)

select
	st_astext(
		(st_dump(
			st_split(
				st_makeline(st_makepoint(0,0),st_makepoint(2,2))
		-- 		, st_makepoint(1,1)
				, st_multi(st_union(st_makepoint(1.5,1.5),st_makepoint(0.5,0.5)))
				)
			)).geom
		)

On Fri, 09 Feb 2018 13:56:10 +0100, Olivier Leprêtre <o.lepretre at gmail.com> wrote:

> Hi, thanks for your answers,
>
>
> I didn't interpret well what st_split would do, I thought st_split(line, set of n points) would returns n+1 set of lines segments but in fact it returns 2 n lines, input line being cut n times. So I have to search another way, likely as Nicolas suggested with st_lineLocatePoint and st_lineSubstring, or using st_split one point at a time.
>
>
> Olivier
>
>
> De : postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] De 
> la part de Alexandre Neto Envoyé : vendredi 9 février 2018 13:31 À : 
> PostGIS Users Discussion Objet : Re: [postgis-users] splitting a 
> linestring with points
>
>
> Beware that hitting a line with a point can be tricky in terms of accuracy. Unless the point is snapped to one of the line's vertices, if you zoom enough, it will not be on top of the line. That may be the reason why you are not getting the desired results.
>
>
> Olivier Leprêtre <o.lepretre at gmail.com> escreveu no dia sexta, 9/02/2018 às 09:55:
>
> Hi Martin
>
> I hoped but it's doesn't with results from 
> st_collectionExtract(st_Split())
>
> Olivier
>
> -----Message d'origine-----
> De : postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] De 
> la part de Martijn Meijers Envoyé : vendredi 9 février 2018 09:15 À : 
> postgis-users at lists.osgeo.org Objet : Re: [postgis-users] splitting a 
> linestring with points
>
> st_dump would make it possible, no?
>
> select st_astext((st_dump('MULTILINESTRING((0 0, 10 10), (20 20, 30 30))')).geom);
>          st_astext
> -------------------------
>   LINESTRING(0 0,10 10)
>   LINESTRING(20 20,30 30)
> (2 rows)
>
>
>
> On 08-02-18 21:48, Olivier Leprêtre wrote:
>>
>> Hi,
>>
>> I want to break a linestring into linestrings by breaking it with a 
>> set of points along this line. This appeared easy at first but 
>> finally, I tried using st_split(line, set of points) but this returns 
>> multilinestrings when I just wants linestrings. I tried several 
>> functions like st_dump, st_geometryN, stcollectionextract and so on 
>> after st_split but did not find how could I get only rows of 
>> linestring splitted by the points acting like blades on the first 
>> linestring.
>>
>> Thanks for any help,
>>
>> Olivier
>>
>>
>> <https://www.avast.com/sig-email?utm_medium=email <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> &utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>>       Garanti sans virus. www.avast.com 
>> <https://www.avast.com/sig-email?utm_medium=email 
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm
>> _campaign=sig-email&utm_content=emailclient> 
>> &utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>>
>>
>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/postgis-users
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/postgis-users
>
>
> ---
> L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast.
> https://www.avast.com/antivirus
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/postgis-users
>


--
Using Opera's mail client: http://www.opera.com/mail/