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On 20/11/2011 12:50, Pankaj Kr Sharma wrote:
<blockquote
cite="mid:CAM5_u0Ee4k4=v99wUxe6S55FTbK4b8aXkwTRqyLs_Rg9j50aGA@mail.gmail.com"
type="cite">Dear Micha,<br>
by the method of threshold value, I have tried and output varies
from 1 sqkm to 6000 sqkm.<br>
Not what I want.<br>
<br>
</blockquote>
<br>
Give us some more information:<br>
g.region -p<br>
r.info <your dem raster><br>
the exact command you used to run r.watersheds<br>
<br>
<br>
<blockquote
cite="mid:CAM5_u0Ee4k4=v99wUxe6S55FTbK4b8aXkwTRqyLs_Rg9j50aGA@mail.gmail.com"
type="cite">
<div class="gmail_quote">On Sun, Nov 20, 2011 at 2:44 PM, Micha
Silver <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:micha@arava.co.il">micha@arava.co.il</a>></span>
wrote:<br>
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<div class="im"> On 20/11/2011 08:58, Pankaj Kr Sharma
wrote:
<blockquote type="cite">
<div>Dear grass users,</div>
<div>I am trying to find sub-basins and their outlets
exactly for each 300 sq. km. in a bigger basin.</div>
<div>I think accumulation value indicates the no. of
cells draining at a cell. And will thus be a good
starting point for such calculation.</div>
</blockquote>
<br>
</div>
The threshold value is what you're looking for. You need to
calculate how many raster cells it will take to make 300 sq.
km - depending on the raster resolution. For example, if the
resolution is 90 m. (i.e. SRTM elevation data) then each
cell = 8100 sq.m. then you will need a threshold of 370,000
to create basins of about 300 <a moz-do-not-send="true"
href="http://sq.km" target="_blank">sq.km</a>.<br>
<br>
<blockquote type="cite">
<div class="im">
<div>The other option is to start backwards from the
basin outlet and keep on investigating upwards in a
stream network.</div>
<div>Can someone provide some hint / help in this
regard.</div>
<div>Thanks.</div>
<br>
</div>
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