Re: [GRASS-user] Watershed delineation result problem
On Wed, 7 Oct 2020, ming han wrote: Thanks for sharing, I see, I will continue with GRASS version I guess. Ming, While I mis-read your 'watershed' as 'wetlands' the same argument holds true. I don't know the size of each cell in your DEM raster or whether arcGIS uses the cell center or a corner for calculations. There are so many factors involved that unless there are major differences pick one and use it. As I run only linux and have used GRASS since the mid-1990s I can't speak about arcGIS. Stay well, Rich ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Watershed delineation result problem
Hi Rich Thanks for sharing, I see, I will continue with GRASS version I guess. Cheers Ming Rich Shepard 于2020年10月7日周三 下午1:42写道： > On Wed, 7 Oct 2020, ming han wrote: > > > Hope this email find you safe and healthy > > > > I tried watershed delineation with both ArcGIS and GRASS. but I got > > different results. > > > > I was using D8 flow direction method in both ArcGIS and GRASS. My study > > area is very flat. Is there any tool in GRASS will generate the same > result > > with ArcGIS > > Ming, > > I did wetland determinations and delineations for almost a decade but > dropped it when it became a commodity. I offer two points for your > consideration: > > 1) The ArcGIS may not be any more 'accurate' than the GRASS results. Never > having used the former I cannot comment on how they do this. > > 2) Of greater importance is that you can pick either one; it doesn't matter > in the real world. In 1994 I was the first environmental consultant > authorized by Oregon's Department of State Lands to use GPS receivers to > delineate wetland boundaries. They had insisted that only professional land > surveyors could do this and they set a 2cm accuracy standard. Really? > Wetland boundaries are transistion zones that can be several meters wide, > depending on topography, soils, and antecedent precipitation conditions > when > the boundary is flagged. A stream bank is an exception to this broad > transition area. When I made the case that there is no sharp line of > demarkation between wetland and upland they accepted my delineations. > > Of similar disconnect between engineering and natural ecosystems, I worked > for a brief time for a water management district in the 1980s. They decided > to digitize the 7.5 min (1:24000) topographic maps covering the District's > area and contracted with a company in India to do the work. The contract > specified that the digitized lines had to aline withine 1/2 the width of > roads and other boundaries on the maps. When I pointed out to my Division > Director that the maps themselves said "this map is accurate to +/- 24 > feet" > so they were trying to be more accurate than the maps themselves it was not > well received. :-) (That's one reason I left a government position.) > > Anyway, draw your boundary and in most cases you'll be within that > transition zone. > > HTH, > > Rich > ___ > grass-user mailing list > grass-user@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Watershed delineation result problem
On Wed, 7 Oct 2020, ming han wrote: Hope this email find you safe and healthy I tried watershed delineation with both ArcGIS and GRASS. but I got different results. I was using D8 flow direction method in both ArcGIS and GRASS. My study area is very flat. Is there any tool in GRASS will generate the same result with ArcGIS Ming, I did wetland determinations and delineations for almost a decade but dropped it when it became a commodity. I offer two points for your consideration: 1) The ArcGIS may not be any more 'accurate' than the GRASS results. Never having used the former I cannot comment on how they do this. 2) Of greater importance is that you can pick either one; it doesn't matter in the real world. In 1994 I was the first environmental consultant authorized by Oregon's Department of State Lands to use GPS receivers to delineate wetland boundaries. They had insisted that only professional land surveyors could do this and they set a 2cm accuracy standard. Really? Wetland boundaries are transistion zones that can be several meters wide, depending on topography, soils, and antecedent precipitation conditions when the boundary is flagged. A stream bank is an exception to this broad transition area. When I made the case that there is no sharp line of demarkation between wetland and upland they accepted my delineations. Of similar disconnect between engineering and natural ecosystems, I worked for a brief time for a water management district in the 1980s. They decided to digitize the 7.5 min (1:24000) topographic maps covering the District's area and contracted with a company in India to do the work. The contract specified that the digitized lines had to aline withine 1/2 the width of roads and other boundaries on the maps. When I pointed out to my Division Director that the maps themselves said "this map is accurate to +/- 24 feet" so they were trying to be more accurate than the maps themselves it was not well received. :-) (That's one reason I left a government position.) Anyway, draw your boundary and in most cases you'll be within that transition zone. HTH, Rich ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Watershed delineation result problem
Hi Everyone Hope this email find you safe and healthy I tried watershed delineation with both ArcGIS and GRASS. but I got different results. I was using D8 flow direction method in both ArcGIS and GRASS. My study area is very flat. Is there any tool in GRASS will generate the same result with ArcGIS Thanks Ming ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] tiled version for r.neighbors
Hi Moritz, thanks for the hacks, they seem very useful!I am not so worried about the speed right now but more with the "do-ability" of the job.For some of the things I tried to do I just got stuck on 0 or 3% and the process did not go further, at least in the simple computers I use.I may try a modification of your code in the coming weeks, it does not seem so hard indeed. I come back here if can (or cannot) do it. Thanks! regardgin the r.patch part, what you mean is that it could be better to have a calll to the module r.patch instead of to this function "rpatch_map" that is used in the source code? BestBernardo Em quarta-feira, 7 de outubro de 2020 13:08:16 GMT+2, Moritz Lennert escreveu: On 7/10/20 12:37, Bernardo Santos wrote: > Dear community, > > I have recently found that some functions such as r.mapcalc and > r.textile have their "tiled" versions, whichi is perfect for processing > things in large extents and fine scale resolution. > I need to perform a moving window analysis, such as using r.neighbors, > over large areas. Is there already any implementation of a > "r.neighbors.tiled" or something like that? > (If not, that would definitely be very useful!) AFAIK, there is no r.neighbors.tiled. Actually, the two others you cite were quick hacks from me which I decided to make available in case they could be useful. Several tests by others using r.mapcalc.tiled have not shown significant speed increase, and so there is currently a discussion about how to solve this (the current idea is to try with r.patch instead of the internal python-based patching routine). Unfortunately, I don't have much time for GRASS GIS these days, so will not be able to do anything about this. You could have a look at the existing *.tiled modules (see link to the code at the bottom of the online man page) to see how they work (not very complicated) and try to cook your own for r.neighbors. :-) Moritz ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] tiled version for r.neighbors
Dear community, I have recently found that some functions such as r.mapcalc and r.textile have their "tiled" versions, whichi is perfect for processing things in large extents and fine scale resolution. I need to perform a moving window analysis, such as using r.neighbors, over large areas. Is there already any implementation of a "r.neighbors.tiled" or something like that?(If not, that would definitely be very useful!) Best wishesBernardo ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] tiled version for r.neighbors
On 7/10/20 12:37, Bernardo Santos wrote: Dear community, I have recently found that some functions such as r.mapcalc and r.textile have their "tiled" versions, whichi is perfect for processing things in large extents and fine scale resolution. I need to perform a moving window analysis, such as using r.neighbors, over large areas. Is there already any implementation of a "r.neighbors.tiled" or something like that? (If not, that would definitely be very useful!) AFAIK, there is no r.neighbors.tiled. Actually, the two others you cite were quick hacks from me which I decided to make available in case they could be useful. Several tests by others using r.mapcalc.tiled have not shown significant speed increase, and so there is currently a discussion about how to solve this (the current idea is to try with r.patch instead of the internal python-based patching routine). Unfortunately, I don't have much time for GRASS GIS these days, so will not be able to do anything about this. You could have a look at the existing *.tiled modules (see link to the code at the bottom of the online man page) to see how they work (not very complicated) and try to cook your own for r.neighbors. :-) Moritz ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
