Re: Bugs in r.stream.extract

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Ming,

The discrepancy in flow accumulation between the two modules is explained
in the r.accumulate manual at
https://grass.osgeo.org/grass78/manuals/addons/r.accumulate.html. See
Examples =3D> Flow accumulation. Most likely, this is because of
r.watershed's handling of border cells.

Thanks,
Huidae

On Wed, Nov 25, 2020 at 7:17 AM ming han <[email protected]> wrote:

> And another problem I got is that the flow accumulation I got from
> r.accumulate and r.watershed is different when r.accumulate using flow
> direction from r.watershed.  Again is there anyway r.watershed supports
> using flow direction, so we can get the consistent result.
>
> We need this when we need to adjust the flow direction from  r.watershed
> or r.stream.extract. and then we need to determine new flow accumulation
> with an adjusted flow direction dataset.  If the result is inconsistent,
> not sure what is the solution is.
>
> Cheers
> Ming
>
> ming han <[email protected]> =E4=BA=8E2020=E5=B9=B411=E6=9C=8825=E6=97=
=A5=E5=91=A8=E4=B8=89 =E4=B8=8A=E5=8D=886:38=E5=86=99=E9=81=93=EF=BC=9A
>
>> Hi Ken
>>
>>    Many thanks for your reply, I think I made a mistake, the flow
>> accumulation I provided to r.stream.extract did not match the DEM I
>> provided in r.stream.extract.  The streamline seems based on flow
>> accumulation derived from the provided DEM.
>>
>>    But, If I only want to use flow direction to drive streams, which
>> function I should use?
>>
>>    Is there any chance that  r.stream.extract can use flow direction as
>> inputs without DEM?
>>
>> Thanks
>> Ming
>>
>>
>> Ken Mankoff <[email protected]> =E4=BA=8E2020=E5=B9=B411=E6=9C=8824=E6=
=97=A5=E5=91=A8=E4=BA=8C =E4=B8=8A=E5=8D=887:07=E5=86=99=E9=81=93=EF=BC=9A
>>
>>> Hi Ming,
>>>
>>> On 2020-11-23 at 09:05 -08, ming han <[email protected]> wrote...
>>> > Hope this email finds you well. I got a weird result when using
>>> > r.stream.extract, as shown in the following figure. The back grids is
>>> > the flow accumulation layer with a flow accumulation threshold larger
>>> > than 1000. while the blue line is the stream generated by
>>> > r.stream.extract. Why the stream from r.stream.extract did not follow
>>> > flow accumulation results? And how to fix this problem?
>>>
>>> Is there any chance you can share the raster that includes this region
>>> so I can examine it? And the exact command you ran?
>>>
>>>   -k.
>>>
>>> _______________________________________________
> grass-dev mailing list
> [email protected]
> https://lists.osgeo.org/mailman/listinfo/grass-dev
>


--=20
Huidae Cho, Ph.D., GISP
GRASS GIS Developer
https://idea.isnew.info

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<div dir=3D"ltr"><div>Ming,</div><div><br></div><div>The discrepancy in flo=
w accumulation between the two modules is explained in the r.accumulate man=
ual at <a href=3D"https://grass.osgeo.org/grass78/manuals/addons/r.accumula=
te.html">https://grass.osgeo.org/grass78/manuals/addons/r.accumulate.html</=
a>. See Examples =3D&gt; Flow accumulation. Most likely, this is because of=
 r.watershed&#39;s handling of border cells.</div><div><br></div><div>Thank=
s,</div><div>Huidae<br></div></div><br><div class=3D"gmail_quote"><div dir=
=3D"ltr" class=3D"gmail_attr">On Wed, Nov 25, 2020 at 7:17 AM ming han &lt;=
<a href=3D"mailto:[email protected]">[email protected]</a>&gt; wrote:<br>=
</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;b=
order-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr">An=
d another problem I got is that the flow accumulation I got from r.accumula=
te and r.watershed is different when r.accumulate using flow direction from=
 r.watershed.=C2=A0 Again is there anyway r.watershed supports using flow d=
irection, so we can get the consistent result.=C2=A0<div><br></div><div>We =
need this when we need to adjust the flow direction from=C2=A0

 r.watershed or r.stream.extract. and then we need to determine new flow ac=
cumulation with an adjusted flow direction dataset.=C2=A0 If the result is =
inconsistent, not sure what is the solution is.=C2=A0</div><div><br></div><=
div>Cheers</div><div>Ming=C2=A0</div></div><br><div class=3D"gmail_quote"><=
div dir=3D"ltr" class=3D"gmail_attr">ming han &lt;<a href=3D"mailto:dustmin=
[email protected]" target=3D"_blank">[email protected]</a>&gt; =E4=BA=8E2020=E5=
=B9=B411=E6=9C=8825=E6=97=A5=E5=91=A8=E4=B8=89 =E4=B8=8A=E5=8D=886:38=E5=86=
=99=E9=81=93=EF=BC=9A<br></div><blockquote class=3D"gmail_quote" style=3D"m=
argin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left=
:1ex"><div dir=3D"ltr">Hi Ken<div><br></div><div>=C2=A0 =C2=A0Many thanks f=
or your reply, I think I made a mistake, the flow accumulation I provided t=
o r.stream.extract did not match the DEM I provided in r.stream.extract.=C2=
=A0 The streamline seems based on flow accumulation derived from the provid=
ed DEM.=C2=A0 =C2=A0</div><div>=C2=A0 =C2=A0=C2=A0</div><div>=C2=A0 =C2=A0B=
ut, If I only want to use flow direction to drive streams, which function I=
 should use?=C2=A0</div><div><br></div><div>=C2=A0 =C2=A0Is there any chanc=
e that=C2=A0

r.stream.extract can use flow direction as inputs without DEM?=C2=A0</div><=
div><br></div><div>Thanks</div><div>Ming=C2=A0=C2=A0</div><div>=C2=A0 =C2=
=A0</div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gma=
il_attr">Ken Mankoff &lt;<a href=3D"mailto:[email protected]" target=3D"_bl=
ank">[email protected]</a>&gt; =E4=BA=8E2020=E5=B9=B411=E6=9C=8824=E6=97=A5=
=E5=91=A8=E4=BA=8C =E4=B8=8A=E5=8D=887:07=E5=86=99=E9=81=93=EF=BC=9A<br></d=
iv><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bord=
er-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Ming,<br>
<br>
On 2020-11-23 at 09:05 -08, ming han &lt;<a href=3D"mailto:[email protected]=
om" target=3D"_blank">[email protected]</a>&gt; wrote...<br>
&gt; Hope this email finds you well. I got a weird result when using<br>
&gt; r.stream.extract, as shown in the following figure. The back grids is<=
br>
&gt; the flow accumulation layer with a flow accumulation threshold larger<=
br>
&gt; than 1000. while the blue line is the stream generated by<br>
&gt; r.stream.extract. Why the stream from r.stream.extract did not follow<=
br>
&gt; flow accumulation results? And how to fix this problem?<br>
<br>
Is there any chance you can share the raster that includes this region so I=
 can examine it? And the exact command you ran?<br>
<br>
=C2=A0 -k.<br>
<br>
</blockquote></div>
</blockquote></div>
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</a><br>
</blockquote></div><br clear=3D"all"><br>-- <br><div dir=3D"ltr" class=3D"g=
mail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr=
"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><span><div><div dir=3D"ltr">H=
uidae Cho, Ph.D., GISP</div><div dir=3D"ltr">GRASS GIS Developer</div><div>=
<a href=3D"https://idea.isnew.info" target=3D"_blank">https://idea.isnew.in=
fo</a><br></div></div></span></div></div></div></div></div></div></div></di=
v></div></div>

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