On Wed, Mar 9, 2016 at 8:28 PM, Bartolomei.Chris <[email protected]> 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.)
If you use r.stream.extract instead of r.watershed + r.thin + r.to.vect + v.clean + etc, you get line directions pointing downstream without any further processing/editing. Please note that r.stream.extract also writes points at stream sources, confluences, and outlets. If you are only interested in vector stream segments, you can extract them with v.extract type=line layer=1 HTH, Markus M > 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 > [email protected] > > The information contained in this email message is intended only for the use > of the individual(s) to whom it is addressed and may contain information that > is privileged and sensitive. If you are not the intended recipient, or > otherwise have received this communication in error, please notify the sender > immediately by email at the above referenced address and note that any > further dissemination, distribution or copying of this communication is > strictly prohibited. > > The U.S. Export Control Laws regulate the export and re-export of technology > originating in the United States. This includes the electronic transmission > of information and software to foreign countries and to certain foreign > nationals. Recipient agrees to abide by these laws and their regulations -- > including the U.S. Department of Commerce Export Administration Regulations > and the U.S. Department of State International Traffic in Arms Regulations -- > and not to transfer, by electronic transmission or otherwise, any content > derived from this email to either a foreign national or a foreign destination > in violation of such laws. > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
