[GRASS-dev] Unresolved directions in r.fill.dir

[Anna Petrášová]

On Sun, Nov 26, 2017 at 4:04 PM, Markus Metz
<markus.metz.giswork at gmail.com> wrote:
> Hi Vaclav,
>
> On Sun, Nov 26, 2017 at 1:31 AM, Vaclav Petras <wenzeslaus at gmail.com> wrote:
>>
>> Hi all,
>>
>> r.fill.dir with the bellow artificial DEM leaves part of the directions
>> unresolved and this area is marked in areas, although the area is filled in
>> the output. Here is the code to reproduce:
>>
>> g.region n=220750 s=220000 w=638300 e=639000 nsres=1 ewres=1 rows=750
>> cols=700 -p
>> r.mapcalc "hills = 500 * sin(row()) + 500 * sin(col())"
>> r.fill.dir input=hills output=filled direction=directions areas=areas
>>
>> In r71809, I have committed a fix which transforms these unresolved
>> directions to NULLs because in the previous implementation (current 7.4svn
>> and older) internal representation of angles was leaking outside of the
>> module.
>>
>> I have 2 questions:
>>
>> Should I backport r71809 to 7.4?
>
> For me, the fix makes sense.
>>
>> Should we pursue this issue further to resolve why these edge cases are
>> not resolved, although they are filled? Does anybody has suggestions at this
>> point? (Paper with the method is linked in the doc.)
>
> I don't think it is worth the pursue the issue of directions any further.
> The module is based on rather old, not to say outdated, methods from the
> 1980's. These methods were developed for DEMs created from contour lines
> which in turn were determined by land surveyors. Back then there was nothing
> like SRTM or LiDAR.
>
> r.hydrodem offers a more advanced method to remove sinks by a combination of
> filling and carving.

Why don't we move r.hydrodem to core? Is there any reason to keep it in addons?

Anna

>
> Directions can also be obtained with r.slope.aspect or with the hydrological
> modules r.watershed, r.stream.extract, r.terraflow. Regarding hydrology,
> main flow directions may differ between modules and settings and to
> directions from r.slope.aspect, but all of them are valid according to the
> logic of the underlying algorithm and settings.
>
> Markus M
>>
>> Thank you,
>> Vaclav
>>
>> https://trac.osgeo.org/grass/changeset/71809
>> https://grass.osgeo.org/grass74/manuals/r.fill.dir.html
>>
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>
>
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