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On 07/13/2012 06:10 PM, Jaime Palalane wrote:
<blockquote
cite="mid:CAKqXksFPn_Eqy7S6qpse9FGd5Oj7t9OjjGhMM-XuXCGZZ8miuQ@mail.gmail.com"
type="cite">Thank you for this prompt reply. One additional
question. Is there any quick way to get a hipsometric curve or
area values between different altitude intervals from a DEM
representing my basin?<br>
<br>
</blockquote>
<br>
I don't know about quick, but here are a few GRASS modules that you
might find helpful.<br>
<br>
<small><font face="Courier New, Courier, monospace"><big><big>r.reclass</big></big></font></small>
can create a new raster from the original DEM broken into steps that
you specify. So you could create a raster with elevation steps of,
say, 50 meters. Now run <small><font face="Courier New, Courier,
monospace"><big><big>r.stats -a</big></big></font></small> on
that raster and you'll get a list of the total area for each value.
This list could be imported into any other software (spreadheet) to
calculate the accumulated areas for each elevation step.<br>
<br>
Another option could be to use <big><font face="Courier New,
Courier, monospace">r.contours</font></big> to create contour
lines at whatever interval is suitable. (There is also the GDAL Tool
<big><font face="Courier New, Courier, monospace">gdal_contour</font></big>
in QGIS, under Raster->Extraction). Now merge the contour lines
with the basin boundary to form closed boundaries around each
elevation "strip", and convert into polygons. And finally, in GRASS
use the <big><font face="Courier New, Courier, monospace">v.rast.stats</font></big>
module to calculate several statistics for each elevation polygon. <br>
<br>
Regards,<br>
Micha<br>
<br>
<br>
<blockquote
cite="mid:CAKqXksFPn_Eqy7S6qpse9FGd5Oj7t9OjjGhMM-XuXCGZZ8miuQ@mail.gmail.com"
type="cite">Jaime<br>
<br>
<br>
<br>
<div class="gmail_quote">2012/7/13 Micha Silver <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:micha@arava.co.il"
target="_blank">micha@arava.co.il</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="direction:ltr" bgcolor="#FFFFFF" text="#000000">
<div class="im"> On 07/13/2012 04:02 PM, Jaime Palalane
wrote:
<blockquote type="cite">Dear qgis users,<br>
<br>
I am trying to use qGIS to characterize a hydrographic
basin but I am facing problems with the profile from
line tool as it is giving an unique altitude value for
my rivers and lengths in grades. I would like to have
them in SI units. I would appreciate some tips in how to
solve this problem.<br>
<br>
</blockquote>
<br>
</div>
The units should be the units of the coordinate system. I
think that if you want altitudes and lengths in meters,
you'll have to project both the raster and the line features
to a projected CRS with meters as units.
<div class="im"><br>
<br>
<blockquote type="cite">I am also trying to use the
r.water.outlet command to define a basin draining to a
specific point of a stream in raster format but without
success as it gives me back only one cell as the basin
and not a combination of cells which could form a real
basin. Any tutorial or video in how to use this command?<br>
<br>
</blockquote>
<br>
</div>
Perhaps the problem is that the outlet point must fall
exactly on a stream. There's a trick using v.distance to
find a drainage point exactly on the stream, described here:<br>
<br>
<a moz-do-not-send="true"
href="http://www.surfaces.co.il/?p=241" target="_blank">http://www.surfaces.co.il/?p=241</a><br>
<br>
First add two columns to the streams layer: outlet_x,
outlet_y. Now use v.distance with your outlet point as the
"from" parameter, and the stream as the "to" parameter. Set
the upload parameter to "to_x,to_y" and the column parameter
to "outlet_x,outlet_y". Now after you run, you should get
the X,Y coordinates of a point *on the stream* nearest to
your planned outlet point. Use those coordinates in your
r.water.outlet command, and you should get the full drainage
area.<br>
<br>
HTH,<br>
Micha<br>
<br>
<blockquote type="cite">Saudaçoes!<br>
<br>
Jaime<br>
<br>
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<br>
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<span class="HOEnZb"><font color="#888888"> </font></span></blockquote>
<span class="HOEnZb"><font color="#888888"> <br>
<br>
<pre cols="72">--
Micha Silver
GIS Consultant, Arava Development Co.
<a moz-do-not-send="true" href="http://www.surfaces.co.il" target="_blank">http://www.surfaces.co.il</a></pre>
</font></span></div>
</blockquote>
</div>
<br>
<br clear="all">
<br>
-- <br>
Jaime Palalane<br>
+258 82 70 56 990<br>
<br>
This mail was received via Mail-SeCure System.<br>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
GIS Consultant, Arava Development Co.
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a></pre>
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