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

[toni hernández]

thanks Hugues,

The thing is that with st_Dump I get all the linestrings of a river but 
there is no way (that I know of) that I can order all the segments and 
get the "real" start /end points of the whole river.

*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 <mailto:toni at sigte.udg.edu>

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

On 09/06/2015 08:56, Hugues François wrote:
>
> 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 <mailto: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
>     <mailto: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 <mailto:toni at sigte.udg.edu>
>
>     http://www.sigte.udg.edu
>     Twitter http://twitter.com/SIGTE_UDG
>
>
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