Micha, No, after looking at what's going-on in more detail, I think the DEM is too coarse (even at 90m), so the flow direction and accumulation is mis-directed in one critical area of the watershed. I tried using r.carve, but it is taking forever — after 15 minutes, no advancement of the progress bar…
I did not want to have to do this for my testing, but I'll probably try at 3 or 10 meter — lots of pixels for my basin! The problem, in general, for me is that I want to apply my techniques at international locations where I probably won't have the benefit of higher resolution DEMs, so I need to develop something a bit more robust… Cheers! Tom On Fri, Feb 13, 2015 at 1:15 PM, Micha Silver <[email protected]> wrote: > > On 02/13/2015 08:48 PM, Thomas Adams wrote: > > Stefan, > > A fair question; since I know the stream topology from personal > experience it is clear that there should be no break in the stream network > and the flow accumulation grid should reflect that. I am seeing the flow > accumulation values break at a point where they should continue to > accumulate downstream. > > > Are these breaks possibly caused by null pixels in the DEM? > > Tom > > On Fri, Feb 13, 2015 at 11:43 AM, Stefan Lüdtke <[email protected]> > wrote: > >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> Hi Tom, >> >> just out of curiosity, what do you mean by "break in the flow >> accumulation"? >> >> Cheers, >> >> Stefan >> >> On 02/13/2015 07:12 PM, Thomas Adams wrote: >> > Hello all! >> > >> > I'm making use of the flow accumulation grid in GRASS 6.4.5 >> > generated from r.watershed using the SFD (D8) flow algorithm. The >> > DEM has a 250m spatial resolution. What I'm getting is a break in >> > the flow accumulation in a few locations which is causing me >> > serious problems with subsequent processing (with help from some >> > here, I have put together some scripting to generate a pixel >> > connectivity file for a distributed hydrologic model). >> > >> > Besides going to a higher resolution DEM, are there any thoughts as >> > to how I can eliminate these flow accumulation breaks? >> > >> > Thank you, Tom >> > >> > -- >> > >> > >> > >> > _______________________________________________ grass-user mailing >> > list [email protected] >> > http://lists.osgeo.org/mailman/listinfo/grass-user >> > >> >> - -- >> Stefan Lüdtke >> >> Section 5.4- Hydrology >> Tel.: +49 331 288 2821 >> Fax: +49 331 288 1570 >> Email: [email protected] >> >> Helmholtz-Zentrum Potsdam >> Deutsches GeoForschungsZentrum GFZ >> (GFZ German Research Centre for Geoscience) >> Stiftung des öff. Rechts Land Brandenburg >> Telegrafenberg, 14473 Potsdam >> - ------------------- >> >> PGP Public Key: http://bit.ly/13d9Sca >> -----BEGIN PGP SIGNATURE----- >> Version: GnuPG v1.4.11 (GNU/Linux) >> >> iQEcBAEBAgAGBQJU3kXYAAoJEB5GAbKcg+D8YqMH/jgJZ70cz69IJal6ICi66wqW >> lQYnnko592KAOlFDu1lReZhWWVgeA59rDsYA2Gg/rBzoL9Nst3hzIJDWqnhIWl3W >> YgF/vOJgTRnrNJtOibGpOc8hxrHwElxU7afYlXU8Zk+4tXdZRK4/vrQ4tKEcbY0z >> MrhAYjR66RRpoNf9/3WJ3s14CpPA+KEkOaysOOoTV6Ni7qZTK8rVxt+svQQoPtW+ >> 5QwRJLkLeM6bUrqfQifHis91j4k3JSoSp7ZjIInKwi1tvCSfcFQhzvANs4x8e1Lo >> Q5wDbzHshhJieGKyraUZyT8cn9vszv9cm2Sf49O/0FWVz3Eyc9vsKFxVcvfEb1E= >> =Sy/3 >> -----END PGP SIGNATURE----- >> > > > > -- > > > > This mail was received via Mail-SeCure System. > > > _______________________________________________ > grass-user mailing > [email protected]http://lists.osgeo.org/mailman/listinfo/grass-user > This mail was received via Mail-SeCure System. > > > > >
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