One more idea is to make sure the DEM is projected. Flow algorithms, in GRASS and ArcGIS, get messed up by unprojected surfaces. Be careful choosing a projection for such a large area. Also projecting should be done after you put the mosaic together, as you may get streaks around the boundaries of the individual DEMs that will affect the flow. Or just run the individual DEMs and assemble the flow maps after. -Thayer From: Daniel Victoria <daniel.victo...@gmail.com> To: Charlie Shobe <chsh5...@colorado.edu> Cc: Thayer Young <thaye...@yahoo.com>; "grass-user@lists.osgeo.org" <grass-user@lists.osgeo.org> Sent: Tuesday, January 13, 2015 10:46 AM Subject: Re: [GRASS-user] r.terraflow on massive DEM Charlie,
I just downloaded some SRTM 1arc sec. from EarthExplorer. The data is supplied in 3 different file types, GeoTIFF, DTED or BIL and they are all in Integer values (Int16). No floating point elevation values. Cheers Daniel On Tue, Jan 13, 2015 at 12:12 PM, Charlie Shobe <chsh5...@colorado.edu> wrote: Hi Daniel, I believe that SRTM data does in fact provide floating point elevation values, so you may want to try working with the DEM as type FCELL from the very beginning. I don't know if this will help solve your problem, but the last time I brought in SRTM (1 arc second) data it was type FCELL and contained several decimal places of precision. Good luck, Charlie On Jan 13, 2015, at 4:00 AM, Daniel Victoria <daniel.victo...@gmail.com> wrote: Stephan, I'll give r.watershed a try and let it run for a couple of days. Thanks Thayer, I used r.recode because the person that sent me the data messed up the null values. So in order to fix that I did: 1) use r.external to bring the data to Grass 2) fix null values with r.recode, which was faster than r.null But I gave up on that path and since imported the data (r.in.gdal) and fixed the null values with r.null. I'm also using integer values (CELL type) because from what I heard, SRTM does not provide floating point data. Now I tried to run r.terraflow but I got a type error which asked me to use r.terraflow.short. Since I don't have that command in my grass instalatin, I converted the SRTM data to float. But that was to no avail since it's now giving me a dimensions type overflow error and asking me to change the dimension_type and recompile. I'll give r.watershed a try. If that does not work, I'll see if I can recompile. Thanks Daniel On Mon, Jan 12, 2015 at 9:22 PM, Thayer Young <thaye...@yahoo.com> wrote: With regards to the size of DEM, if you can get the command to run it may take several days to finish, this is more than twice the size of the Washington State DEM that took the authors 33 hours in 2003 (Arge, Chase, Halpin, Toma, Urban, Vitter, Wickremesinghe Efficient Flow Computation on Massive Grid Terrain Datasets Geoinformatica Volume 7 Issue 4, December 2003 Pages 283 - 313 ). My mid-2014 computer runs at about twice the speed quoted in the paper. Did you r.recode it to make it smaller? In flat areas you need the data contained after the decimal point to allow the flow a chance to make it down hill, otherwise you can get streams going no where near where they do in real life. I have never tried running r.terraflow on an integer raster, I know that it works on decimal rasters. -Thayer Date: Mon, 12 Jan 2015 09:59:40 -0200 From: Daniel Victoria <daniel.victo...@gmail.com> To: grass <grass-user@lists.osgeo.org> Subject: [GRASS-user] r.terraflow on massive DEM Message-ID: <CA+irsJjf7xhWgU968D+4+xc2YGJ=_n4xjtp0_weu1zportt...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hi list, I'm trying to run r.terraflow on a very large DEM but I wander if it's __too large__. The region dimensions are: ncol=141114 nrow=140487 Data type = CELL The map is actually a reclass map of a raster that I imported using r.external. When I run r.terraflow I get: r.terraflow elevation=srtm_brasil@PERMANENT filled=srtm_fill direction=flowdir swatershed=sink accumulation=flowacc tci=srtm_tci directory=E:\terraflow_temp WARNING: raster srtm_brasil is of type CELL_TYPE --you should use r.terraflow.short ERROR: [nrows=140487, ncols=141114] dimension_type overflow -- change dimension_type and recompile (Mon Jan 12 09:57:18 2015) Command finished (0 sec) However, I don't have an r.terraflow.short command I'm running Grass 7.0.0beta4 from OsGeo4W Cheers Daniel -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20150112/a27c139f/attachment-0001.html> ------------------------------ _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user End of grass-user Digest, Vol 105, Issue 16 ******************************************* _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
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