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<div class="moz-cite-prefix">On 07/16/2013 04:28 PM, Elisa Dal Maso
wrote:<br>
</div>
<blockquote
cite="mid:CABb8FvD+1=dLDkS95vBA6_n7gYJzE4Egwex8t0dY8BpQ3wWy+Q@mail.gmail.com"
type="cite">
<div dir="ltr">Hi, I'm a PhD student in Italy and I am a new user
of GRASS.
<div style="">I have a problem in a weighted average with
r.mapcalc.</div>
<div style="">There are 3 raster map (areas of species), with
different extent but the same resolution, area has value 1,
outside is null *.</div>
<div style="">I would like to sum these areas with different
weights (10, 9 and 4), then divide for the sum of weights
(23), generating a float, and I have used this formula:</div>
<div style=""><br>
</div>
<div style="">(10.*if(isnull(Fraxinus_excelsior_raster@Phalaen),
0, 1)+9.*if(isnull(Fraxinus_angustifolia_raster@Phalaen), 0,
1) +4.*if(isnull(Fraxinus_ornus_raster@Phalaen), 0, 1))/23.<br>
</div>
<div style=""><br>
</div>
</div>
</blockquote>
<br>
Instead of the "isnull()" functions, just set null to '0' with
r.null for each raster before your mapcalc expression: i.e.<br>
r.null Fraxinus_excelsior_raster null=0 <br>
same for each of the other Fraxious* ...<br>
then, be sure you have set the region correctly:<br>
g.region rast=`g.mlist type=rast pattern="Frax*" separator=,`<br>
and finally<br>
r.mapcalc "weighted = (Fraxinus_excelsior_raster * 10.0 + ....+
....)/23.0"<br>
<br>
<blockquote
cite="mid:CABb8FvD+1=dLDkS95vBA6_n7gYJzE4Egwex8t0dY8BpQ3wWy+Q@mail.gmail.com"
type="cite">
<div dir="ltr">
<div style="">The resulting map have only 4 rectangles but it
considers the sum of all the map (null values comprised).</div>
<div style=""><br>
</div>
<div style="">How could I resolve the problem?</div>
<div style="">
Thanks a lot!!!</div>
<div style=""><br>
</div>
<div style="">Elisa</div>
<div style=""><br>
</div>
<div style=""><br>
</div>
</div>
<br>
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</blockquote>
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