<span style="font-family:arial,helvetica,sans-serif; font-size:12px">The 
problem was that I hadn't imported my layers in GRASS, they were only in QGIS, 
so r.mapcalc had nothing to work on...&nbsp;<br>
I made in work in GRASS (without QGIS) and it worked perfectly.<br>
<br>
Thank you very much for your help.<br>
<br>
Marion</span>

<div class="gl_quote" style="margin-top: 20px; padding-top: 5px;">De : "Markus 
Neteler"<br>
A : [email protected],"grass-user"<br>
Envoyé: lundi 2 juillet 2018 23:59<br>
Objet : Re: [GRASS-user] how to use r.mapcalc in GRASS<br>
&nbsp;
<div class="gl_quoted">Hello Marion,<br>
<br>
On Mon, Jul 2, 2018 at 12:18 PM, marion-brunet wrote:<br>
&gt; Hello,<br>
&gt;<br>
&gt; I am trying to calculate the difference between two raster layers. For 
that,<br>
&gt; I am using GRASS in QGIS. I use the command r.mapcalc. In the field<br>
&gt; "expression to evaluate" I wrote<br>
&gt; r.mapcalc expression=diff =TIN_12_17-TIN_06_18<br>
<br>
be sure to have white spaces around the - (minus)<br>
<br>
TIN_12_17-TIN_06_18<br>
--&gt; TIN_12_17 - TIN_06_18<br>
<br>
and, as Vero wrote, perhaps quotes. So, pls try:<br>
<br>
r.mapcalc expression="diff =TIN_12_17 - TIN_06_18"<br>
<br>
Best,<br>
Markus</div>

<div class="gl_quoted">&nbsp;</div>
</div>
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