[GRASS-user] Networks

[achim]

achim schrieb:
> 
> 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?

-how can I distinguish between points and polylines?
to add a layer you can set a geometry type (eg. type=point) and do a
"v.category" (misleading name) in an additional layer
v.category --overwrite input=network at achim output=network at achim
type=point layer=2
if you did it wrong before adding all geometries, you can delete
(option=del) some of the categories
v.category --overwrite input=network at achim output=network at achim
option=del type=line layer=2

(I feel a bit schizo)

Questions remaining:
-> 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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