[GRASS-dev] stream from grass is inconsistent with streams from ArcGIS

GRASS GRASS developer
1

Hi Everyone

I just notice that streams from GRASS are inconsistent with streams obtained from ArcGIS sometimes, when there is a flat or low slope dem region such as lakes.

As shown in the following figure, there is a sharp turn from streams derived from GRASS.

I love GRASS and I am a GRASS user, I am asking this because the DEM that I am using is MERIT hydrological pre-conditioned DEM. I guess they are using ArcGIS.

I just want to get a consistent stream network with the stream network provided by MERIT.

Is there any solution for this?

Many thanks
Ming

image.png

2

Dear Ming,

what function are you using to derive the streams in GRASS?

The reason is probably that GRASS and ArcGIS use different algorithms to obtain the streams from the dem. As far as I remember (but I might be wrong) ArcGIS uses SFD while GRASS (r.stream.extract) uses MFD (i.e. single vs. multiple flow directions).

So, if you want to get exactly the same streams you need to find out how ArcGIS does it and try to set the parameters in GRASS accordingly (of possible).

Additionally, flat areas are usually difficult for all algorithms.

Best,

Mira

(attachments)

image.jpg

···

On 17/02/2021 16.23, ming han wrote:

Hi Everyone

I just notice that streams from GRASS are inconsistent with streams obtained from ArcGIS sometimes, when there is a flat or low slope dem region such as lakes.

As shown in the following figure, there is a sharp turn from streams derived from GRASS.

I love GRASS and I am a GRASS user, I am asking this because the DEM that I am using is MERIT hydrological pre-conditioned DEM. I guess they are using ArcGIS.

I just want to get a consistent stream network with the stream network provided by MERIT.

Is there any solution for this?

Many thanks
Ming

image.png

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Dr. Mira Kattwinkel
Quantitative Landscape Ecology
iES Landau, Institute for Environmental Sciences
University of Koblenz-Landau
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76829 Landau
Germany
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