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
-------- Original message --------
From: Etienne DELAY
Date:26/10/2015 15:15 (GMT+01:00)
To: Markus Neteler
Cc: GRASS user list
Subject: Re: [GRASS-user] river and dams in netwok analysis
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
<etienne.delay@etu.unilim.fr mailto:etienne.delay@etu.unilim.fr> 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_ShapefileWARNING: 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,boundaryhttps://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#ScreenshotsBest
Markus
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