[GRASS-user] v.net vector orientation when creating a stream network with gauges

[Will Fields]

Hi Chris,

d.vect has an option to display the direction of lines, and the vector
digitizer has a tool to flip the direction of things.  The man pages have
details about those things work.

Regards,

Will

On Wed, Mar 9, 2016 at 2:28 PM, Bartolomei.Chris <Bartolomei.Chris at ensco.com
> wrote:

> Good afternoon,
> I was hoping someone could provide some insight as to how v.net works.  I
> have a set of (438) watershed boundaries and their DEMs from which I have
> created the stream vectors from the DEM rasters (r.watershed, r.thin,
> r.to.vect, v.clean, etc.)  I also have the set of USGS stream gauges as
> points from which I extract the gauges within each watershed as a separate
> map. I am able to use v.net op=connect to create a network with the
> stream vectors and watershed gauge points no problem and v.path
> successfully creates paths from one gauge to the next IF the forward and
> backward costs are the same (cost is length).
> What I am trying to do is measure the distance between a pair of gauges
> that are in the same flow path. I am automating this so there is no user
> input as to which pair to select, therefore I would like to use
> v.net.allpairs and then analyze the resulting table and select only those
> which have a route.
> If I set the fwd cost to length and the backwards cost to -1 to shut off
> going upstream after traversing downstream, then the paths fail – which in
> many cases is good, but the paths between gauges that are clearly
> up/downstream from each other (along the same flow path) fail as well. If I
> reverse the forward and backward cost columns the path calculations still
> fail.
> My thoughts are that the stream vectors do not have the correct forward
> and/or backward orientation (they are probably mixed) in the network. Is
> there a way to see or set the orientation of the stream vectors? Does
> anyone have experience with this?
> When I created the stream vectors, I didn’t include the 3D data, if it
> were included in the stream vector would the forward/backward orientation
> then go from higher elevation to lower?
>
> I’ve looked at (
> https://grasswiki.osgeo.org/wiki/Vector_extract_upstream_network) and I
> seem to lose a lot of (stream) lines when the network is created this way
> which I feel may be related to the vector orientations as well.
>
> Any assistance would be greatly appreciated!
> 
> Chris
>
>
>
> Chris Bartolomei P.E.
> Engineer/Scientist
> ENSCO, Inc.
> 4849 North Wickham Road
> Melbourne, FL 32940 (official office)
> 5038 Park Rim Drive
> San Diego, CA 92117 (home office)
> (858) 581-3005
> bartolomei.chris at ensco.com
>
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