<div dir="ltr"><div>Ming,</div><div><br></div><div>The discrepancy in flow accumulation between the two modules is explained in the r.accumulate manual at <a href="https://grass.osgeo.org/grass78/manuals/addons/r.accumulate.html">https://grass.osgeo.org/grass78/manuals/addons/r.accumulate.html</a>. See Examples => Flow accumulation. Most likely, this is because of r.watershed's handling of border cells.</div><div><br></div><div>Thanks,</div><div>Huidae<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Nov 25, 2020 at 7:17 AM ming han <<a href="mailto:dustming@gmail.com">dustming@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">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. <div><br></div><div>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. </div><div><br></div><div>Cheers</div><div>Ming </div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">ming han <<a href="mailto:dustming@gmail.com" target="_blank">dustming@gmail.com</a>> 于2020年11月25日周三 上午6:38写道：<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Hi Ken<div><br></div><div> 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. </div><div> </div><div> But, If I only want to use flow direction to drive streams, which function I should use? </div><div><br></div><div> Is there any chance that
r.stream.extract can use flow direction as inputs without DEM? </div><div><br></div><div>Thanks</div><div>Ming </div><div> </div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Ken Mankoff <<a href="mailto:mankoff@gmail.com" target="_blank">mankoff@gmail.com</a>> 于2020年11月24日周二 上午7:07写道：<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Ming,<br>
<br>
On 2020-11-23 at 09:05 -08, ming han <<a href="mailto:dustming@gmail.com" target="_blank">dustming@gmail.com</a>> wrote...<br>
> Hope this email finds you well. I got a weird result when using<br>
> r.stream.extract, as shown in the following figure. The back grids is<br>
> the flow accumulation layer with a flow accumulation threshold larger<br>
> than 1000. while the blue line is the stream generated by<br>
> r.stream.extract. Why the stream from r.stream.extract did not follow<br>
> 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>
-k.<br>
<br>
</blockquote></div>
</blockquote></div>
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</blockquote></div><br clear="all"><br>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><span><div><div dir="ltr">Huidae Cho, Ph.D., GISP</div><div dir="ltr">GRASS GIS Developer</div><div><a href="https://idea.isnew.info" target="_blank">https://idea.isnew.info</a><br></div></div></span></div></div></div></div></div></div></div></div></div></div>