On Wednesday 23 January 2008, [EMAIL PROTECTED] wrote: > Thanks for pointing out the excerpt from the manual. So, based on > that it seems that r.watershed will take longer to run than the > ArcHydro tools. How much longer? I guess I will just let it run and > see if I can find out. Then I will run r.terraflow and compare the > differences between ArcHydro, r.terrafow and r.watershed. > > If anyone has used r.watershed on a comparably sized DEM, I would be > interested to hear how long it took to run. By the way my machine has > a 2.8Ghz P4 processor and 1.25G of RAM.
Here is a small comparison I did a while back on watershed delineation, comparing r.watershed, r.terraflow, and basin from Arc/Info: http://casoilresource.lawr.ucdavis.edu/drupal/node/284 note that it is a little sparse on the details, and could use some better figures. see code examples for explanation. cheers, Dylan > Quoting M S <[EMAIL PROTECTED]>: > > If you are in a relatively flat area, there needs to be consideration > > given to the algorithm (to my knowledge there is no "choice" in the > > ArcGIS suite) used to do the most important thing: delineate the > > watershed basin. Since the question was asked about differences, this > > may apply if your terrain is relatively flat. > > > > From the r.watershed manual, "If watershed divides contain flat to low > > slope, *r.watershed* will generate better basin results than > > *r.terraflow*. (*r.terraflow* uses the same type of algorithm as ESRI's > > ArcGIS watershed software which fails under these conditions.)" > > http://download.osgeo.org/grass/grass63/manuals/html63_user/r.watershed.h > >tml > > > > > > Mark > > > > On Jan 23, 2008 11:42 AM, <[EMAIL PROTECTED]> wrote: > >> Thanks. I will try and change my threshold value this evening. > >> > >> A little background, I have completed this phase of the project at > >> "work" using ArcHydro and it took about half a day total to run > >> through the tools (fill, flow direction, flow accumulation, etc.). I > >> am trying to now do the same project at home using open source tools > >> as a means of learning grass and as a comparison. I wonder if the > >> r.watershed algorithms differ enough from the ArcHydro ones to make > >> execution times very different? Any thoughts? > >> > >> Quoting Charles Ehlschlaeger <[EMAIL PROTECTED]>: > >> > r.watershed will take a long time for a 8,600x10,300 cell DEM under > >> > any circumstance. Your threshold value (400) might also be slowing > >> > things > >> > >> down. > >> > >> > How large should your smallest exterior watershed basin be? If your > >> > grid cells are 10mx10m, your basins will be 400x10mx10m = 40,000 m^2: > >> > not > >> > >> that > >> > >> > large. The larger the th value, the faster the program will run. > >> > > >> > Sincerely, chuck > >> > > >> > Chuck Ehlschlaeger, Geospatial Science Consultant > >> > PERTAN GROUP, http://pertan.com/ > >> > [EMAIL PROTECTED], 309-255-2727 > >> > http://chuck.ehlschlaeger.info/ > >> > > >> > > >> > -----Original Message----- > >> > From: [EMAIL PROTECTED] > >> > [mailto:[EMAIL PROTECTED] On Behalf Of > >> > [EMAIL PROTECTED] > >> > Sent: Wednesday, January 23, 2008 8:52 AM > >> > To: Charles Ehlschlaeger > >> > Cc: [email protected] > >> > Subject: RE: [GRASS-user] Use of r.watershed > >> > > >> > Chuck, > >> > > >> > Thanks for your reply. The DEM has 8,627 rows and 10,270 columns. > >> > The command line statement I used is: > >> > > >> > r.watershed el=fill th=400 ac=fac ba=basins st=str > >> > > >> > I have also tried using the -m and -4 flags placed after the > >> > r.watershed part. > >> > > >> > Thanks, > >> > > >> > Matt > >> > > >> > Quoting Charles Ehlschlaeger <[EMAIL PROTECTED]>: > >> >> How many rows and columns are in the input map? Also include the > >> >> exact command line statement you use to run the program. > >> >> > >> >> Sincerely, chuck > >> >> > >> >> Chuck Ehlschlaeger, Geospatial Science Consultant > >> >> PERTAN GROUP, http://pertan.com/ > >> >> [EMAIL PROTECTED], 309-255-2727 > >> >> http://chuck.ehlschlaeger.info/ > >> >> > >> >> > >> >> -----Original Message----- > >> >> From: [EMAIL PROTECTED] > >> >> [mailto:[EMAIL PROTECTED] On Behalf Of > >> >> [EMAIL PROTECTED] > >> >> Sent: Wednesday, January 23, 2008 7:15 AM > >> >> To: [email protected] > >> >> Subject: [GRASS-user] Use of r.watershed > >> >> > >> >> Hello All, > >> >> > >> >> I am new to GRASS but have been using GIS (mainly ESRI products) for > >> >> quite a few years. I am trying to learn how to use GRASS to carry > >> >> out hydrology related analyses. Currently, I am trying to use the > >> >> r.watershed command to delineate the basins for a watershed. My > >> >> question is, how long would you expect it to take to run? I am > >> >> wondering if I am doing it wrong or if it just takes longer than I > >> >> would expect. The DEM is about 170MB TIFF before I import it to > >> >> GRASS. I have tried to run it a few times using different options, > >> >> each time letting it run for 3 - 4 hours before killing it. I have > >> >> tried both the -m and -4 flags. Any input would be appreciated. > >> >> _______________________________________________ > >> >> grass-user mailing list > >> >> [email protected] > >> >> http://lists.osgeo.org/mailman/listinfo/grass-user > >> >> > >> >> No virus found in this incoming message. > >> >> Checked by AVG Free Edition. > >> >> Version: 7.5.516 / Virus Database: 269.19.9/1238 - Release Date: > >> > >> 1/22/2008 > >> > >> >> 8:12 PM > >> >> > >> >> > >> >> No virus found in this outgoing message. > >> >> Checked by AVG Free Edition. > >> >> Version: 7.5.516 / Virus Database: 269.19.9/1238 - Release Date: > >> > >> 1/22/2008 > >> > >> >> 8:12 PM > >> > > >> > _______________________________________________ > >> > grass-user mailing list > >> > [email protected] > >> > http://lists.osgeo.org/mailman/listinfo/grass-user > >> > > >> > No virus found in this incoming message. > >> > Checked by AVG Free Edition. > >> > Version: 7.5.516 / Virus Database: 269.19.9/1238 - Release Date: > >> > >> 1/22/2008 > >> > >> > 8:12 PM > >> > > >> > > >> > No virus found in this outgoing message. > >> > Checked by AVG Free Edition. > >> > Version: 7.5.516 / Virus Database: 269.19.9/1238 - Release Date: > >> > >> 1/22/2008 > >> > >> > 8:12 PM > >> > >> _______________________________________________ > >> 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 -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
