[GRASSLIST:2809] Re: continued problems with v.net.alloc

Radim Blazek blazek at itc.it
Tue Mar 2 12:43:29 EST 2004

On Saturday 28 February 2004 18:53, Christopher Fonnesbeck wrote:
> I am trying to extract a continuous stream layer from a fragmented
> layer using v.net.alloc and v.extract, following the 5.7 tutorial, but
> have yet to replicate the results properly. I have  a vector layer
> derived from a terraflow accumulation raster. In trying to extract the
> largest contiguous network, I digitized a point "outlet" near the
> outlet of the watershed, then derived a vector to connect the point to
> the network using v.distance. The stream layer, outlet point and
> connecting vector were the joined using v.patch:
> v.patch input=streams_clean,outlet_to_streams,outlet out=streams_outlet
> I then ran v.net.alloc to try and allocate subnets:
> v.net.alloc in=streams_outlet out=streams_alloc nfield=1 ccats=1
> However, when I then try to extract the largest subnet with v.extract,
> it does not work. That is, I get only 2 subnets, the connecting vector
> used in v.patch (cat=0) and the entire stream network (cat=1),
> including the disconnected fragments! I thought v.net.alloc was
> supposed to allocate connected regions to subnets, yet this is not what
> is happening (apparently). What am I doing wrong?

It should work as you expect. Could you send me your streams_outlet?


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