Re: [GRASS-user] Filling sinks w/ minimum slope
On 2017-06-20 at 08:45, Markus Metz wrote: > Negative values in the drainage direction should only occur at the > borders of the current region and around NULL cells. Note that if you > want internal sinks to be drained, you must not use the depression > option. I was not using depression option but I have determined that the mask I was using had a few NULLs in it that I was not aware of. I think this was the problem. Thank you for assisting, -k. ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Filling sinks w/ minimum slope
Hi Ken, To my knowledge r.watershed does not require to fill sinks in advance, because it has a minimal impact routing for handling (non-real) sinks. Do you have a particular reason for your wish to fill the DEM in advance? Cheers Stefan -Original Message- From: grass-user [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of Ken Mankoff Sent: mandag 19. juni 2017 18.36 To: GRASS user list Subject: [GRASS-user] Filling sinks w/ minimum slope Hi GRASS list, I'm interested in filling sinks in a DEM before using r.watershed. I currently use r.fill.dir. I've discovered that the SAGA fill command has an option to set a "Minimum slope gradient to preserve from cell to cell; with a value of zero sinks are filled up to the spill elevation (which results in flat areas)" (see http://www.saga-gis.org/saga_tool_doc/2.1.3/ta_preprocessor_4.html ). Does anyone know of an option for this in GRASS, or an addon that implements this feature? I've briefly looked at calling SAGA from GRASS and it seems non-trivial. I'd prefer to do this in GRASS if possible. Thanks, -k. ___ 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] Filling sinks w/ minimum slope
On Tue, Jun 20, 2017 at 10:05 AM, Ken Mankoff wrote: > > > On 2017-06-20 at 06:28, Markus Metz wrote: > > You don't need to fill sinks with r.watershed, internal sinks are by > > default drained. > > I have negative values in the drainage direction raster produced by r.watershed in the interior. Is this a bug? Or am I misunderstanding the definition of a sink? Negative values in the drainage direction should only occur at the borders of the current region and around NULL cells. Note that if you want internal sinks to be drained, you must not use the depression option. > > While looking into this, I also notice that I get different accumulation maps if I scale the elevation (e.g. divide by 100), even when using the "-s" flag. At first consideration, this does not make sense to me. There could be small differences due to floating point representation differences. > > > You can create flat areas (also with r.terraflow), then use the -b > > flag of r.watershed to create a gentle slope for flat areas. > > I tried this and the accumulation map still has end-points (and direction has negative values) in the interior. Accumulation stops only if true sinks are defined with the depression option or if the elevation of any neighbor is unknown (border of the current region, NULL cells). I tested with elev_lid792_1m in the NC dataset and don't get negative drainage in internal sinks: g.region -p rast=elev_lid792_1m r.watershed ele=elev_lid792_1m drain=elev_lid792_1m_drain acc=elev_lid792_1m_acc Markus M ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Filling sinks w/ minimum slope
On 2017-06-20 at 06:28, Markus Metz wrote: > You don't need to fill sinks with r.watershed, internal sinks are by > default drained. I have negative values in the drainage direction raster produced by r.watershed in the interior. Is this a bug? Or am I misunderstanding the definition of a sink? While looking into this, I also notice that I get different accumulation maps if I scale the elevation (e.g. divide by 100), even when using the "-s" flag. At first consideration, this does not make sense to me. > You can create flat areas (also with r.terraflow), then use the -b > flag of r.watershed to create a gentle slope for flat areas. I tried this and the accumulation map still has end-points (and direction has negative values) in the interior. -k. ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Filling sinks w/ minimum slope
On Mon, Jun 19, 2017 at 10:35 PM, Ken Mankoff wrote: > > > On 2017-06-19 at 18:20, Stefan Blumentrath wrote: > > To my knowledge r.watershed does not require to fill sinks in advance, > > because it has a minimal impact routing for handling (non-real) sinks. > > > > Do you have a particular reason for your wish to fill the DEM in > > advance? > > If I don't fill it, then my definition of non-real and the algorithms definition are different. I need all water to leave the domain, but there are internal sinks. You don't need to fill sinks with r.watershed, internal sinks are by default drained. You could also use r.hydrodem to remove internal sinks. > My solution is to fill them like this: > > # run the filling algorithm until there are no holes left > A=1 > while [[ $A -ne 0 ]]; do > r.fill.dir input=phi output=phi format=agnps direction=d areas=a --o --q > A=$(r.info a | egrep -o "max = .*" | cut -c7-20) > done > g.remove -f type=raster name=a,d > > Then use "phi" as the elevation input to r.watershed. Then all water leaves the domain, but there are flat areas. I would prefer if these were gently-sloped. A colleague does this in QGIS w/ SAGA and the minimum slope, but I am trying to make the work reproducible, and therefore prefer CLI GRASS to GUI QGIS. You can create flat areas (also with r.terraflow), then use the -b flag of r.watershed to create a gentle slope for flat areas. Markus M > > -k. > ___ > 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] Filling sinks w/ minimum slope
On 2017-06-19 at 18:20, Stefan Blumentrath wrote: > To my knowledge r.watershed does not require to fill sinks in advance, > because it has a minimal impact routing for handling (non-real) sinks. > > Do you have a particular reason for your wish to fill the DEM in > advance? If I don't fill it, then my definition of non-real and the algorithms definition are different. I need all water to leave the domain, but there are internal sinks. My solution is to fill them like this: # run the filling algorithm until there are no holes left A=1 while [[ $A -ne 0 ]]; do r.fill.dir input=phi output=phi format=agnps direction=d areas=a --o --q A=$(r.info a | egrep -o "max = .*" | cut -c7-20) done g.remove -f type=raster name=a,d Then use "phi" as the elevation input to r.watershed. Then all water leaves the domain, but there are flat areas. I would prefer if these were gently-sloped. A colleague does this in QGIS w/ SAGA and the minimum slope, but I am trying to make the work reproducible, and therefore prefer CLI GRASS to GUI QGIS. -k. ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
