[GRASS-dev] [GRASS GIS] #2980: r.watershed and max_slope_length

#2980: r.watershed and max_slope_length
---------------------+-------------------------
Reporter: mankoff | Owner: grass-dev@…
     Type: defect | Status: new
Priority: normal | Milestone: 7.0.4
Component: Raster | Version: 7.0.1
Keywords: | CPU: OSX/Intel
Platform: MacOSX |
---------------------+-------------------------
I'm not sure if this is a bug, but I think it might be. The
{{{max_slope_length}}} seems to have no effect in the {{{r.watershed}}}
program. Below is an example that should work on the NC data set. I'd
expect there to be different accumulation maps based on setting
{{{max_slope_length}}}, but they appear identical.

{{{
r.mapcalc "rain = 1"
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc
drainage=fdir flow=rain
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc.len
drainage=fdir.len flow=rain max_slope_length=15
g.gui.mapswipe first=acc second=acc.len
}}}

Also mentioned at https://www.mail-archive.com/grass-
user@lists.osgeo.org/msg31665.html and
https://gis.stackexchange.com/questions/187312/what-does-the-max-slope-
length-option-do-in-grass-r-watershed

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2980&gt;
GRASS GIS <https://grass.osgeo.org>

#2980: r.watershed and max_slope_length
------------------------+-------------------------
  Reporter: mankoff | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone: 7.0.4
Component: Raster | Version: 7.0.1
Resolution: | Keywords: r.watershed
       CPU: OSX/Intel | Platform: MacOSX
------------------------+-------------------------
Changes (by martinl):

* keywords: => r.watershed

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2980#comment:1&gt;
GRASS GIS <https://grass.osgeo.org>

#2980: r.watershed and max_slope_length
------------------------+-------------------------
  Reporter: mankoff | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone: 7.0.4
Component: Docs | Version: 7.0.1
Resolution: | Keywords: r.watershed
       CPU: OSX/Intel | Platform: MacOSX
------------------------+-------------------------
Changes (by mankoff):

* component: Raster => Docs

Comment:

Turns out that this works, but only influences the length_slope output,
not the accumulation output, which is why the example above doesn't appear
to work.

Source: https://gis.stackexchange.com/questions/187312/what-does-the-max-
slope-length-option-do-in-grass-r-watershed

In this case, this could be considered a documentation bug?

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2980#comment:2&gt;
GRASS GIS <https://grass.osgeo.org>

#2980: r.watershed and max_slope_length
------------------------+-------------------------
  Reporter: mankoff | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone: 7.0.4
Component: Docs | Version: 7.0.1
Resolution: | Keywords: r.watershed
       CPU: OSX/Intel | Platform: MacOSX
------------------------+-------------------------

Comment (by mmetz):

Replying to [ticket:2980 mankoff]:
> I'm not sure if this is a bug, but I think it might be. The
{{{max_slope_length}}} seems to have no effect in the {{{r.watershed}}}
program. Below is an example that should work on the NC data set. I'd
expect there to be different accumulation maps based on setting
{{{max_slope_length}}}, but they appear identical.

The `max_slope_length` option only affects RUSLE outputs `length_slope`
and `slope_steepness`. From the manual: "This input is used for the RUSLE
calculations".

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2980#comment:3&gt;
GRASS GIS <https://grass.osgeo.org>

#2980: r.watershed and max_slope_length
-------------------------+-------------------------
  Reporter: mankoff | Owner: grass-dev@…
      Type: defect | Status: closed
  Priority: normal | Milestone: 7.0.7
Component: Docs | Version: 7.0.1
Resolution: worksforme | Keywords: r.watershed
       CPU: OSX/Intel | Platform: MacOSX
-------------------------+-------------------------
Changes (by mankoff):

* status: new => closed
* resolution: => worksforme

Comment:

This issue was submitted many years ago and appears to be due to my
misunderstanding some of the features of r.watershed and RUSLE.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2980#comment:7&gt;
GRASS GIS <https://grass.osgeo.org>