[GRASS-dev] r.terraflow vs. r.hydrodem

Stefan Blumentrath Stefan.Blumentrath at nina.no
Fri Jun 14 13:03:02 PDT 2019


Before investing time in getting r.terraflow to work on larger regions I actually tried r.fill.dir.

The problem is that the results are significantly different and those of r.terraflow and r.hydrodem (where no breaching is performed) are more suitable for my needs. Here, r.terraflow fills most, r.fill.dir least and r.hydrodem inbetween.

Here a little comparison based on NC data:

g.extension extension=r.hydrodem operation=add
g.region -p raster=elevation

r.fill.dir --overwrite --verbose input=elevation output=elevation_fill_dir_depressionless direction=elevation_fill_dir_direction areas=elevation_fill_dir_pas

r.hydrodem -a --overwrite input=elevation memory=5000 output=elevation_hydrodem_depressionless

r.terraflow --overwrite --verbose elevation=elevation filled=elevation_terraflow_depressionless memory=5000

for m in terraflow fill_dir hydrodem
r.mapcalc --o expression="${m}_effect=if((elevation_${m}_depressionless-elevation)>0,elevation_${m}_depressionless-elevation,null())"

r.univar map="terraflow_effect"
total null and non-null cells: 2025000
total null cells: 1901290

Of the non-null cells:
n: 123710
minimum: 7.62939e-06
maximum: 12.5168
range: 12.5168
mean: 1.49711
mean of absolute values: 1.49711
standard deviation: 1.97871
variance: 3.91528
variation coefficient: 132.169 %
sum: 185206.976940155

r.univar map="fill_dir_effect"
total null and non-null cells: 2025000
total null cells: 1964852

Of the non-null cells:
n: 60148
minimum: 7.62939e-06
maximum: 10.9003
range: 10.9003
mean: 0.499953
mean of absolute values: 0.499953
standard deviation: 0.939429
variance: 0.882526
variation coefficient: 187.903 %
sum: 30071.1971092224

r.univar map="hydrodem_effect"
total null and non-null cells: 2025000
total null cells: 1020396

Of the non-null cells:
n: 1004604
minimum: 3.8147e-06
maximum: 4.74686
range: 4.74685
mean: 0.00587574
mean of absolute values: 0.00587574
standard deviation: 0.08715
variance: 0.00759513
variation coefficient: 1483.22 %
sum: 5902.79515457153

Fra: Markus Metz <markus.metz.giswork at gmail.com>
Sendt: fredag 14. juni 2019 14.25
Til: Stefan Blumentrath
Kopi: grass-dev at lists.osgeo.org
Emne: Re: [GRASS-dev] r.terraflow vs. r.hydrodem

On Fri, Jun 14, 2019 at 1:23 PM Stefan Blumentrath <Stefan.Blumentrath at nina.no<mailto:Stefan.Blumentrath at nina.no>> wrote:
> Hi,
> While trying to make r.terraflow work with larger regions, I was wondering if it would be doable to add a flag to r.hydrodem that forces the module to perform only sink filling and no breaching / carving?
> Sink filling is the function I need from r.terraflow but if it would be an option to add this function to r.hydrodem, that would be fine as well of course...

what about r.fill.dir? It should work as is with larger regions.

Markus M

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