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

[toni hernández]

Remi,

I didn't tell you before but I want to use the main river line as the 
line for labeling river's name. So an approximation to the main river is 
good enough for me.
For a major number of cases (rivers tend to be quite linear), I can use 
the st_longestline to get an approximation for the start/end points and 
from there I can use the routing functions.

Thanks.
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 09/06/2015 08:09, toni hernández wrote:
> 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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