> What is good guidance for where to set the threshold? Try using some already existing data for mapped streams, such as the national hydrography dataset. You can adjust the threshold of the accumulation until your modeled output is close to already mapped features.
I don't see the -b flag for r.watershed > 6.4svn checkout (probably a week ago) in the man pages. I think the -b option starts in version 7 (?) I said > realistic because you can set the threshold to 1 for a 1m res dem. > There are lines that don't even look like streams all over the place. Threshold relates to the accumulation of upgradient cells. Its usually a larger number in the thousands to 10s of thousands (at least from my data/experience). > Is it possible to extract streams with the landscape (Mongomery) as a > guide for the threshold? Try without altering the montgomery exponent and see how well it matches known features. Mark > > On Thu, Aug 5, 2010 at 9:35 AM, Jarek Jasiewicz <jar...@amu.edu.pl> wrote: >> stephen sefick pisze: >>> >>> I would like to use the Montgomery method to extract streams (exp~2 >>> from the paper). What should the threshold value be? And in general >>> what should the threshold value be? I am working in the southeastern >>> coastal plain (USA), which is characterized by low gradient (if this >>> helps). >> >> for flat areas Montgomery's method is not a good option. Generally that >> method was created and tested on areas with gradient > 5%. >>> >>> I am using 1m resolution LIDAR data. I would like to extract >>> the most realistic map of streams that I can. >> >> Chmmm... what you mean realistic? Maybe use existing stream network will be >> the best solution? >> For coastal plains where is no real vallyes the r.watershed's treeshold with >> -b option seems to be best option >>> >>> I am also trying to >>> track down the inttermitance perminance threshold. Any guidance would >>> be greatly appreciated. >>> kindest regards, >>> >>> >> >> > > > > -- > Stephen Sefick > ____________________________________ > | Auburn University | > | Department of Biological Sciences | > | 331 Funchess Hall | > | Auburn, Alabama | > | 36849 | > |___________________________________| > | sas0...@auburn.edu | > | http://www.auburn.edu/~sas0025 | > |___________________________________| > > Let's not spend our time and resources thinking about things that are > so little or so large that all they really do for us is puff us up and > make us feel like gods. We are mammals, and have not exhausted the > annoying little problems of being mammals. > > -K. Mullis > _______________________________________________ > 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
