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<div class="moz-cite-prefix">On 09/08/2013 21:15, Admin wrote:<br>
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<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D">Hi Mitch <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks for your
prompt response’<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I have a raster
that covers the whole area and the grid I am talking about
is a square polygon as shown in the pic attached. I want
average slope for each of the polygons<o:p></o:p></span></p>
</div>
</blockquote>
<p><br>
</p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">(Keeping
this on the maillist <font color="rgb(102, 0, 0)">insures
that you'll get the best answers, and helps others along the
way)</font></font></font></p>
<p><br>
</p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">OK, you can
<font color="rgb(102, 0, 0)">get the average slope for each <font
color="rgb(102, 0, 0)">polygon "grid" sq<font
color="rgb(102, 0, 0)">uare as follows:</font></font></font></font></font></p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">Start the
GRASS Tools plugin, and use the wizard to define a GRASS
LOCATION with the same co<font color="rgb(102, 0, 0)">ordinate
system as your DEM raster and polygon lay<font
color="rgb(102, 0, 0)">ers. </font></font></font></font></p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">Now use the
GRASS modules r.in.gdal to import the DEM into GRASS, and
v.in.ogr to import the polygon layer. Once yo<font
color="rgb(102, 0, 0)">u have these two layers in GRASS, </font>run
the GRASS module r.slope.aspect on the DEM raster to create a
slope <font color="rgb(102, 0, 0)">raster</font> from the
DEM.</font></font></p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">Now use v.<font
color="rgb(102, 0, 0)"></font>rast.stats to get several
addition<font color="rgb(102, 0, 0)">al attribute columns into
your polygon (grid squares) layer with the max<font
color="rgb(102, 0, 0)">, min, avg, stddev, etc of slope
from the slope r<font color="rgb(102, 0, 0)">aster.</font></font></font></font></font></p>
<p><br>
</p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">If<font
color="rgb(102, 0, 0)"> necessary, you can export the
polygon (grid squares) with all the new attribute columns
back out to a new shapefile with v.out.ogr.</font></font></font></p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif"><br>
</font></font></p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif">HTH</font></font></p>
<p><br>
</p>
<p><br>
</p>
<p><font color="rgb(102, 0, 0)"><font face="sans-serif"> </font></font><br>
</p>
<blockquote
cite="mid:!&!AAAAAAAAAAAYAAAAAAAAAG+QzjzdGUNEtmYcS16YDAHCgAAAEAAAAGhjscCP9BhIkXDvt%2FuGrWIBAAAAAA==@shaw.ca"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I hope this
will make it clear<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you very
much again<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Moges <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
Micha Silver [<a class="moz-txt-link-freetext" href="mailto:micha@arava.co.il">mailto:micha@arava.co.il</a>] <br>
<b>Sent:</b> August 9, 2013 11:05 AM<br>
<b>To:</b> Admin<br>
<b>Cc:</b> qgis-user<br>
<b>Subject:</b> Re: [Qgis-user] grid avevarage slope<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">On 08/09/2013 07:31 PM, Admin wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#1F497D">Thanks a lot
Micha,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I am not
that efficient in gis. I tried to follow your instruction
but I could not import DEM file to GRASS</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I am using
QGIS 1.8.0-Lisboa , installed GRASS plugins but could not
import DEM data. </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">To make it
clear, I have a basin of about 600 sq km. my model is
run on 15 km x 15 km grid. Some part of the grid falls
outside of the basin boundary apparently. I have 25 grids
in total and I am looking for average slope for 25 grids,
those out of basin are set to 0 anyways. I created
slope map from DEM using raster terrain analysis but to
grid them into 15x15km and find average slope for each
grid is my problem</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Arial","sans-serif"">Sorry,
but I guess I misunderstood. When you say "25 grids" are
these 25 tiles that cover the whole basin? or large grid
cells of 15 km resolution? </span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Arial","sans-serif"">Your
question "grid them into 15x15km ... " makes me think you
mean square polygons of 15km on each side. Is this your
situation? So you want to find the average slope in each of
the 15x15 polygon squares? GOing back to GRASS, there is a
module "v.rast.stats" that calculates various statistics
from a raster for each polygon in a polygon vector layer.
That might be what you need.</span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Arial","sans-serif""> </span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Arial","sans-serif"">Perhaps
if you could mention what original data you have, then
someone on the list could offer a specific work flow. Do you
have an elevation raster? a slope raster? Have you
delineated the actual basin boundary?</span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><o:p> </o:p></span></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I highly
appreciate your help</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Moges</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
Micha Silver [<a moz-do-not-send="true"
href="mailto:micha@arava.co.il">mailto:micha@arava.co.il</a>]
<br>
<b>Sent:</b> August 9, 2013 5:31 AM<br>
<b>To:</b> Admin<br>
<b>Cc:</b> <a moz-do-not-send="true"
href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a><br>
<b>Subject:</b> Re: [Qgis-user] grid avevarage slope</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"> <o:p></o:p></p>
<div>
<p class="MsoNormal">On 08/08/2013 04:57 AM, Admin wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Hi all,<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I need your help. I am working on a
basin. The model I am working with entails average surface
slope on grid basis. My basin has a number of grids. I
clipped and tried to get average slope but I am not happy
with the results.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Is there anyway I can do it? <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
</blockquote>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New Roman
, serif","serif"">Using GRASS is one
approach. If you don't yet have a slope grid, then import
it into GRASS, and run the GRASS module r.slope aspect on
your elevation grid. Then clip it to the basin area. Now
run the r.univar module on the clipped slope grid to get a
set of univariate statistics from the grid.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New Roman
, serif","serif"">If you already have a
clipped slope grid then import that into GRASS, and try
the same r.univar to get the stats.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New Roman
, serif","serif"">Note that there is also a
group of GRASS addons for basin analysis: r.stream.* One
of the addons is r.stream.stats which gives you lots of
basin statistics, including two different approaches to
"average" slope in a watershed.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New Roman
, serif","serif""> </span><o:p></o:p></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Moges<o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman , serif","serif""><br>
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<pre>_______________________________________________<o:p></o:p></pre>
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</blockquote>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New Roman
, serif","serif""><br>
<br>
<br>
<br>
</span><o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>Micha Silver<o:p></o:p></pre>
<pre>GIS Consultant, Arava Development Co.<o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a><o:p></o:p></pre>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><br>
<br>
This mail was received via Mail-SeCure System.<o:p></o:p></span></p>
</blockquote>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif""><br>
<br>
<br>
<o:p></o:p></span></p>
<pre>-- <o:p></o:p></pre>
<pre>Micha Silver<o:p></o:p></pre>
<pre>GIS Consultant, Arava Development Co.<o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a><o:p></o:p></pre>
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This mail was received via Mail-SeCure System.<br>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
GIS Consulting
052-3665918
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a>
</pre>
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