[GRASSLIST:2661] Re: eliminating stream fragments

[Radim Blazek]

On Monday 16 February 2004 20:45, Christopher Fonnesbeck wrote:
> On Feb 16, 2004, at 1:40 PM, Radim Blazek wrote:
> >> How does one "place points" with v.net.alloc? I have browsed the
> >> documentation, and assume it has something to do with the ccats
> >> argument, but am not clear what this argument does, based on the
> >> examples given in the html docs.
> >
> > Sorry, not at any node but at one node (one point). You have to do that
> > by hand in v.digit.
>
> Well, I do have a point layer of bridges that I combined with the
> stream layer using v.patch (see attached figure). However, when I use
> v.net.alloc with one or more of the bridges on the network, I get a
> whole series of "dglShortestPath error: Head Node Not Found" errors,
> and the resulting output layer is no smaller than the original, despite
> several breaks in the original network. Am I missing a step?

Most probably the points are not precisely on nodes, try to run 
v.net operation=report, output is something like:
1 1 2      ( line 1 from point 1 to point 2)
2 2 3
3 2 4
WARNING: Point not found: 1333.333 -1041.667 0.000 line category: 4
WARNING: Point not found: 7708.333 -5083.333 0.000 line category: 4
4 0 0      ( no point at the ends of lin 4)

do you have any line where from/to are not 0? For example
x 0 90, if yes use this point's category for ccats.
Then, I think, that you can ignore dgl* messages.
The whole original map is written to output, but only lines connected
to the point have assigned the category (of that point).
d.vect cats=90; v.extract list=90

Radim