Hi Etienne,
Maybe you could use v.net.allpairs with negative/positve costs for up- and
downstream direction and then select the smallest positive and negative
distance for each dam to get the two neighbours.
Here what I found in the manual of v.net.distance which might also be useful
for your purpose:
"In order to find nearest neighbors within a group of nodes, you can either
loop through each node as to and all other nodes as from or create a complete
distance matrix with v.net.allpairs and select the lowest non-zero distance for
each node."
https://grass.osgeo.org/grass70/manuals/v.net.distance.html
Maybe a start...
/Johannes
<div>-------- Original message --------</div><div>From: Etienne DELAY
<[email protected]> </div><div>Date:26/10/2015 15:15 (GMT+01:00)
</div><div>To: Markus Neteler <[email protected]> </div><div>Cc: GRASS user
list <[email protected]> </div><div>Subject: Re: [GRASS-user] river
and dams in netwok analysis </div><div>
</div>Dear all dear Markus,
Above all great job GRASS dev team ! Grass 7 is so nice and powerful.
I'm always in the dark with my dams problem.
I would like to export dams points as node and for each node in the
attribute table 2 new column : dam before | dam after. I'm looking for
network analysis but it may be a wrong way ?
There is a way to do that in Grass?
Cordialement
Etienne DELAY (Skype : etienne.delay.tic)
Chaire: Capital environnemental et gestion durable des cours d'eau
laboratoire GEOLAB UMR 6042 CNRS
Université de Limoges, FLSH
39E rue Camille Guérin 87036 Limoges
blog : http://elcep.legtux.org
Le 18/10/2015 17:30, Markus Neteler a écrit :
> On Sat, Oct 17, 2015 at 11:17 AM, Etienne DELAY
> <[email protected] <mailto:[email protected]>> wrote:
> > Re,
> > I have read carefully the v.out.ogr as will said for tring to export the
> > network layer but I've got an error :
> >
> > v.out.ogr --overwrite input=network@PERMANENT type=point dsn=~/ layer=2
> > format=ESRI_Shapefile
> >
> > WARNING: 111738 line(s) found, but not requested to be exported. Verify
> > 'type' parameter.
> ...
>
> (I guess that you need to set "type=line" and not "type=point")
>
> ... this is why you may consider to upgrade to the current 7.0.x stable
> version. Note the differences:
>
> https://grass.osgeo.org/grass64/manuals/v.out.ogr.html
> type=string[,string,...] Feature type(s).
> Combinations not supported by all output formats. Default: first type
> found in input.
> Options: point,line,boundary,centroid,area,face,kernel,auto
> Default: line,boundary
>
> https://grass.osgeo.org/grass70/manuals/v.out.ogr.html
> type=string[,string,...] Feature type(s)
> Combination of types is not supported by all output formats.
> Default is to use first type found in input vector map.
> Options: point, line, boundary, centroid, area, face, kernel, auto
> Default: auto <<==
>
> Less to think about, much faster vector data processing, improved
> network analysis along with new graphical frontend:
> https://grasswiki.osgeo.org/wiki/Vector_network_analysis#Screenshots
>
> Best
> Markus
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