<p>Hi Andre,</p>
<p>On raster algebra, operations using null will return null while operations with 0 behaves like expected. Ex:<br>
12 x null = null<br>
12 x 0 = 0</p>
<p>Null is interesting to use on areas you don't have / want to represent, like an ocean...</p>
<p>Hope it helps<br>
Daniel</p>
<div class="gmail_quote">On Feb 5, 2012 12:03 AM, "ALT SHN" <<a href="mailto:i.geografica@alt-shn.org">i.geografica@alt-shn.org</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello,<br><br>I have a technichal doubt. I used<b> v.to.rast.constant </b>to tranform a line vector layer to raster. This meant i have a raster with NULL values. <br>The output raster is to be used in map algebra operations.<br clear="all">
<br>So my question is: Is it advisable to set the Null cells to 0? I know r.calc works with NULL values, and I know that NULL is not the same as 0, however I never understood what difference does it make if any. Considering these two scenarios what do I win and what do I loose?<br>
<br>Any enlightening will be very aprecciated!<br><br>Thanks,<br><br>André Mano <br>---------------------------------------------------------------<br>Associação Leonel Trindade<br>SOCIEDADE DE HISTÓRIA NATURAL<br><br>Apartado 25 <a href="tel:2564-909" value="+5072564909" target="_blank">2564-909</a> Torres Vedras Portugal<br>
Sede e Biblioteca: rua Cavaleiros da Espora Dourada, 27A 2560 Torres Vedras<br><br>Laboratório de Paleontologia e Paleoecologia: Polígono Industrial do Alto do Ameal <a href="tel:2565-641" value="+5072565641" target="_blank">2565-641</a> Ramalhal<br>
<a href="http://alt-shn.blogspot.com" target="_blank">http://alt-shn.blogspot.com</a><br>
<a href="http://www.alt-shn.org" target="_blank">www.alt-shn.org</a><br>
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