[GRASS-user] Networks

achim ak7 at jupiter.uni-freiburg.de
Fri Jun 5 04:50:55 EDT 2009

achim schrieb:
> Hi,
> I am going to do some work on drainage networks I created. I could not
> figure out some basic procedures. Maybe, you have some ideas how to work
> with some of the following questions/tasks:
> 1) how is a network stored? creating it via v.net from a multiline "map"
> says it wants to create two layers: one with lines, the other with points
>  -> general problem: creating an table containing an entry for every
> object (Id). I know thats general, but why doesn't it work with
> v.db.newtable? And why answers v.to.db option=cat with
> "Reading features... Updating database... 0 categories read from vector
> map (layer 1) 0 records updated/inserted (layer 1)"?

to 1)
make sure, the map is connected to the desired database. if necessary
overwrite current connection and delete tables
-> db.droptable -f table=network
-> v.db.connect -d map=network at achim
then do a
-> v.db.addtable map=network at achim layer=1
all geometry objects get a number
(maybe a v.category is necessary before)

 -> Questions remaining:
-how can I distinguish between points and polylines?
-how are connections (polyline)-node-(polyline/polyline) stored/defined?

> 2) how can I identify each network by eg. an integer value? There are
> many unconnected trees, which I want to keep separated.
>  -> I tried it with v.buffer, on the one hand I couldn't upload the
> information to the network (points and polylines) and on the other hand
> it takes a lot of time.
> 3) can I define a "direction" of a network with values on the nodes?
> like a sorted tree? in order to get the sub trees?
> 4) how can I find out, which and how many lines are connected to a node?
> 5) ...there are some, but I think its enough; and furthermore the
> questions more or less depend on each other.
> Hoping, someone has some experience with that kind of stuff,
> kindly regards,
> Achim
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