[GRASS-user] flow accumulation (GRASS and Esri ArcGIS)

[Anna Petrášová]

On Wed, May 2, 2018 at 2:21 PM, Markus Neteler <neteler at osgeo.org> wrote:
> On Wed, May 2, 2018 at 7:13 PM, Martin Landa <landa.martin at gmail.com> wrote:
>> Hi,
>>
>> one of my colleague is dealing with flow accumulation calculation in
>> GRASS, and comparing results with Esri ArcGIS (builtin Flow
>> Accumulation [1]). Tool in ArcGIS to me knowledge uses D8, so we run
>> r.watershed with -s flag and also -a flag to avoid negative values.
>> Resultant values are very different.
>>
>> * Esri ArcGIS (range: 0 - 20741)
>> * r.watershed -s (range: -34068 - 5697)
>> * r.watershed -sa (1 - 34068)
>
> I'd suggest to look at the univariate statistics first (r.univar -e)
> and compare that instead of min/max only.

Also, r.watershed uses least-cost path, unlike the arcmap tool. Did
you fill the depressions before running the arcmap tool?

Anna

>
> markusN
>
>> Do you have idea why results are so different? Thanks for any pointers
>> in advance! Martin
>>
>> [1] http://desktop.arcgis.com/en/arcmap/10.5/tools/spatial-analyst-toolbox/flow-accumulation.htm
>>
>> --
>> Martin Landa
>> http://geo.fsv.cvut.cz/gwiki/Landa
>> http://gismentors.cz/mentors/landa
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>
>
>
> --
> Markus Neteler, PhD
> http://www.mundialis.de - free data with free software
> http://grass.osgeo.org
> http://courses.neteler.org/blog
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