Hi, I'd like to re-open a quite old thread about breaking lines in a network.
the old thread:
>If each line is a straight line, then you have two nodes, one at each end.
>>So, do you mean that you want to break the longer line, thus creating two
>>new nodes, representing the new end points of the two parts and then snap
>>these two nodes back together again and snap a third node (from the other
>>line) to that same place ?
>
>If that is what you want to do, you can use the 'connect' tool in v.edit
>>>(see "Connect lines" in the man page).
>
>If you want to break you line at the coordinates of a specific node, you >can
>do it this way:
>
>v.edit tool=break cat=CatOfTheLineToBreak coords=CoordinatesOfYourNode >thresh=
>v.edit tool=snap cat=CatOfTheBrokenLine,CatOfOtherLine thresh
>
>You can get the coordinates of your nodes with v.to.db.
>Hope this helps,
>Moritz
I am in a similar situation: There is the main stem of a river and a
contributing tributary. I want to break the main stem at the point where the
tributary joins the it. I attached a screenshot with the Cat-numbers as labels
and the selected section of the main stem I'd like to break (yellow).
I considered three ways:
1) Use v.clean with first snapping the tributary to the mainstem and then
breaking at the intersection. But I am not sure if this works as is is not an
intersection (line just joins but don't intersect)!?
2) Using Moritz' approaches with v.edit - connect. Thats what I also tried but
without success so far.
v.edit map=Treene_test@SDM_Treene tool=connect thresh=100,100,100 cats=768,883
Selecting features...
2 of 1336 features selected from vector map <Treene_test@SDM_Treene>
Threshold value for snapping is 100.00
0 lines connected
Building topology for vector map <Treene_test>...
3) or with getting the end point of the tributary (v.to.db) and then use break
(v.edit) and setting the ID to the section of the mainstem (and setting the
threshold).
I already tried also this approach and then some basic questions arose:
(a) What is the difference between Cat and ID. When I break the line (with
v.edit) I get only two IDs but these are actually not two lines (which can e.g.
be selected with the "Query vector map tool" in the GUI).
(b) What is a suitable threshold (10,10,10?) Can there be a to large threshold
if it is snapped to the nearest feature?
(c) Is it useful to set the snap flag in v.edit in such cases? Or should I use
the snap tool (v.edit) as a second process.
(d) As I want two "real" new lines (cats) which show the same attributes, what
is the easiest way to go. The connect tool sounds that this should do that job
but somehow I fail?
Best regards,
Johannes
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<<attachment: Line_to_break.png>>
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