[postgis-users] Get only the main river. Smoothline???

[Hugues François]

Hello,

 

I think ST_Dump could help to deal with multilinestrings: http://postgis.net/docs/ST_Dump.html

 

Hugues.

 

 

De : postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] De la part de toni hernández
Envoyé : mardi 9 juin 2015 08:09
À : postgis-users at lists.osgeo.org
Objet : Re: [postgis-users] Get only the main river. Smoothline???

 

Thanks Remi,

I thought that but I have no starting/ending points. St_StartPoint and St_EndPoint are not working with MultiLinestrings
I'll give it some more intense thought. :)

Cheers.

Toni Hernández Vallès 
Servei de Sistemes d'Informació Geogràfica i Teledetecció
-
Universitat de Girona
SIGTE
-
Pl. Ferrater Mora 1
17071 Girona
Tel +34 972 418 039 (7026 intern)
toni at sigte.udg.edu 

http://www.sigte.udg.edu
Twitter http://twitter.com/SIGTE_UDG

On 08/06/2015 17:45, Rémi Cura wrote:

	if you have start and end point of geom B,
	you can get the river path with a shortest path method (one liner using python, can be done in few hours using plpgsql).

	The idea is that you cut your geom into segments(pairs of points)
	, the length of the segment is the weight of this edge 
	, and you know which segment is connected to which segment (adjacency graph).

	Then you use Networkx <http://networkx.lanl.gov/reference/generated/networkx.algorithms.shortest_paths.generic.shortest_path.html#networkx.algorithms.shortest_paths.generic.shortest_path> shortest path distance.

	
	Else, 

	you are up to use some nasty workaround I suppose (playing with buffers on your original river surface, testing which segment intersects etc. ).

	I tried that but it ends up being more work (and more corner cases) than doing the things properly (in my experience).

	Cheers,

	Rémi-C

	 

	2015-06-08 16:42 GMT+02:00 toni hernández <toni at sigte.udg.edu>:

	Hi everyone,
	
	I have a multilinestring with a river and all its afluents as you can see in this image 
	http://sigserver4.udg.edu/apps/geometries.png
	
	I got geometry A using St_StraithSkeleton.
	
	Is there a way to go from geometry A to geometry B?? 
	Maybe something similar to SmoothLine???
	
	

	-- 
	Toni Hernández Vallès 
	Servei de Sistemes d'Informació Geogràfica i Teledetecció
	-
	Universitat de Girona
	SIGTE
	-
	Pl. Ferrater Mora 1
	17071 Girona
	Tel +34 972 418 039 (7026 intern)
	toni at sigte.udg.edu 
	
	http://www.sigte.udg.edu
	Twitter http://twitter.com/SIGTE_UDG

	
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