<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Hi Micha,</div><div><br></div><div>I understand what you wrote (I think). I get that the basin product from r.watershed does not change with SFD or MFD. I think this is because the flow direction raster from r.watershed only provides the primary flow direction.</div><div><br></div><div>But the accumulation map doesn't know about boundaries or basins, does it? At a divide, can water can flow equally in all 8 directions? If so, I think that at the boundary of the basin delineated by r.water.outlet there may be a cell that contributed 49%. The flow direction would show this cell flows away from the basin boundary because 51% of it does do that, so it is not in the basin. If I use this basin as a mask, I'm losing 49% of that cell, and the many upstream cells that contribute to it. </div><div><br></div><div>The inefficient method, running r.watershed 14,000 times, never considers basins and is therefore not impacted by this issue. </div><div><br> -k. <div><br></div><div>Please excuse brevity. Sent from pocket computer with tiny non-haptic feedback keyboard. </div></div><div><br>On 31 Aug 2017, at 21:18, Micha Silver <<a href="mailto:tsvibar@gmail.com">tsvibar@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
The r.water.outlet module takes as input a flow direction raster
that needs to be created first by r.watershed. So the SFD/MFD
question is irrelevant at this stage. When you first ran r.watershed
you chose which method to use for determining flow direction for
each pixel. Further, SFD/MFD influences only the stream routing, not
the total number of cells in the basin. I'm pretty sure that if you
run r.watershed once with MFD and again with SFD, you'll get the
same basin, only with slightly different stream networks. <br>
AFAIK there should never be a situation where water is directed out
of the basin. So all cells that flow into cell C are then directed
downstream to your final drainage point.<br>
<br>
<div class="moz-cite-prefix">On 08/31/2017 10:04 PM, Ken Mankoff
wrote:<br>
</div>
<blockquote type="cite" cite="mid:81312416-5630-44ED-9B5B-EBC2CCF0FE42@gmail.com">
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<div>Yes. This! What you wrote. </div>
<div><br>
</div>
<div>But the issue is that r.water.outlet make basins based on
SFD, right? What if there are 10,000 cells that feed into cell C
at x,y, and then cell C feeds 49% (based on MFD) into the basin.
These 10,000 cells are not included in the r.water.outlet basin,
are they?<br>
<br>
-k.
<div><br>
</div>
<div>Please excuse brevity. Sent from pocket computer with tiny
non-haptic feedback keyboard. </div>
</div>
<div><br>
On 31 Aug 2017, at 20:51, Micha Silver <<a href="mailto:tsvibar@gmail.com" moz-do-not-send="true">tsvibar@gmail.com</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8">
I'm also not clear what you are asking. But risking a guess:<br>
You could run r.water.outlet *1 time* to get the basin. Then
use that raster as a MASK, so that the next process will
address only the pixels within the basin. Now do a loop with
r.univar on all 14,000 flow rasters, and you'll get 14,000
results with total, min, max, mean, etc of the basin pixels
for each of the flow rasters.<br>
<br>
--<br>
Micha<br>
<br>
<div class="moz-cite-prefix">On 08/31/2017 09:30 PM, Thomas
Adams wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAGxgkWhJ8PWAh+Av1u5KUcLHvqa5NZZvqx+SQzJ0eVz2h3e-0A@mail.gmail.com">
<div dir="ltr">
<div>
<div>Ken,<br>
<br>
</div>
You "want 14,000 values" of what?? Your original email
stated you were "trying to determine flow past a
drainage basin outlet" -- r.watershed does NOT do this,
if indeed this is what you want. And you say you have
"14,000 flow rasters to be used as input" -- what
exactly are these 'flow rasters'; what is your goal? I
may not understand...<br>
<br>
</div>
Tom<br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Aug 31, 2017 at 2:24
PM, Ken Mankoff <span dir="ltr"><<a href="mailto:mankoff@gmail.com" target="_blank" moz-do-not-send="true">mankoff@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="auto">
<div>Hi Tom,</div>
<div><br>
</div>
<div>I have 1 DEM and 14,000 flow rasters to be
used as input. I want 14,000 values, one at a
specific coordinate from each acc output. </div>
<div><br>
</div>
<div>I can do this by running r.watershed 14,000
times. That is slow, unless I'm missing
something (e.g. It works with I.group variables
or Time Series data more efficiently). </div>
<div><br>
</div>
<div>An alternative approach is possible if I knew
the complete drainage basin *and* the fractional
value of each cell that contributed to the
basin. In this case I don't need to route. But
basins from r.watershed or r.water.outlet, I
think, use SFD not MFD (no cell is ever in 2
basins, are they?), and I don't know how to get
the fractional contribution from each cell. </div>
<div><br>
-k.
<div><br>
</div>
<div>Please excuse brevity. Sent from pocket
computer with tiny non-haptic feedback
keyboard. </div>
</div>
<div>
<div class="gmail-h5">
<div><br>
On 31 Aug 2017, at 19:59, Thomas Adams <<a href="mailto:tea3rd@gmail.com" target="_blank" moz-do-not-send="true">tea3rd@gmail.com</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div dir="ltr">
<div>
<div>
<div>Ken,<br>
<br>
</div>
I'm confused about what you are
trying to do with r.watershed,
because the output from the module
is:<br>
<br>
accumulation=name <br>
Name for output accumulation raster
map <br>
Number of cells that drain through
each cell <br>
tci=name <br>
Name for output topographic index
ln(a / tan(b)) map <br>
spi=name <br>
Stream power index a * tan(b) <br>
Name for output raster map <br>
drainage=name <br>
Name for output drainage direction
raster map <br>
basin=name <br>
Name for output basins raster map <br>
stream=name <br>
Name for output stream segments
raster map <br>
half_basin=name <br>
Name for output half basins raster
map <br>
Each half-basin is given a unique
value <br>
length_slope=name <br>
Name for output slope length raster
map <br>
Slope length and steepness (LS)
factor for USLE <br>
slope_steepness=name <br>
Name for output slope steepness
raster map <br>
Slope steepness (S) factor for USLE
<br>
<br>
</div>
I think you want a hydrologic model,
and r.watershed is NOT that. What are
you trying to obtain?<br>
<br>
</div>
Tom<br>
<div>
<div><br>
<br>
<br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Aug
31, 2017 at 1:47 PM, Ken Mankoff <span dir="ltr"><<a href="mailto:mankoff@gmail.com" target="_blank" moz-do-not-send="true">mankoff@gmail.com</a>></span>
wrote:<br>
<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 List,
<div><br>
</div>
<div>I'm trying to determine
flow past a drainage basin
outlet. The complicating
factor is that I need to do
this each day for 40 years. If
I do "r.watershed" ~14,000
times I'll get the results,
but it will take 3 days. It
seems that r.watershed is
likely calculating many things
each time through the loop. Is
there a more efficient way to
this? A flag to r.watershed
that isn't documented?
Something with time-series?</div>
<div><br>
</div>
<div>Alternatively, because I
only need the flow at the
outlet, I could calculate the
basin, not route the flow, and
instead sum the values in the
basin. I assume this would
take seconds or minutes rather
than days. In this case I'm
not sure of the best way to
define the basin. I tried
doing r.water.outlet upstream
from the outlet, but I think
this uses SFD, which means the
basin may be significantly
underestimated.</div>
<div><br>
</div>
<div>I also tried
inverting/flipping the DEM and
then running r.watershed with
convergence=1, and a flow
equal to 0 everywhere except
1000 at the outlet (now the
source due to the inversion)
to see where it flooded
upstream (now downstream due
to the inversion). This didn't
seem to work... because basins
are filled and flow routes to
the edge of the DEM, I could
not pick out the </div>
<div><br>
</div>
<div>Any advice how to either a)
efficiently route 14,000 FLOW
rasters over 1 DEM or b)
determine the full basin will
be much appreciated.</div>
<div><br>
</div>
<div>Thanks,</div>
<div><br>
</div>
<div> -k.</div>
</div>
<br>
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<br>
<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
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</blockquote>
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<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
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