Moritz,<br><br>I really thank you for taking the time to discuss this.<br><br><div class="gmail_quote">On Wed, Jan 23, 2013 at 2:54 PM, Moritz Lennert <span dir="ltr"><<a href="mailto:mlennert@club.worldonline.be" target="_blank">mlennert@club.worldonline.be</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On 23/01/13 13:59, Margherita Di Leo wrote:<br>
</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
Hi Moritz,<br>
<br>
thank you for your reply,<br>
<br>
On Wed, Jan 23, 2013 at 12:21 PM, Moritz Lennert<br></div><div class="im">
<<a href="mailto:mlennert@club.worldonline.be" target="_blank">mlennert@club.worldonline.be</a> <mailto:<a href="mailto:mlennert@club.worldonline.be" target="_blank">mlennert@club.<u></u>worldonline.be</a>>> wrote:<br>
<br>
<br>
If we call WIND the direction map which uses the convention degrees<br>
clockwise from North, and GRASS the output map, the rule that I<br>
applied is:<br>
<br>
IF 0 <= WIND < 270 ; GRASS = 270 - WIND<br>
IF WIND = 270 ; GRASS = 360<br>
IF 270 < WIND < 360 ; GRASS 630 - 0<br>
IF WIND = null ; GRASS = 0<br>
NULL otherwise (this latter I have added to check if there is<br>
any error.<br>
<br>
<br>
This is not correct.<br>
<br>
WIND = 0 means North.<br>
<br>
<br>
Actually this was tricky also for me, but:<br>
<br>
Wind direction is measured in:<br>
<br>
*<br>
<br>
degrees clockwise from uphill (direction the wind is pushing the fire)<br>
<br>
*<br>
<br>
degrees clockwise from North (direction the wind is blowing from)<br>
<br>
If the wind is blowing FROM north, it means that the arrow is TOWARDS<br>
south.. Am I wrong?<br>
</div></blockquote>
<br>
I guess not, but this is a very specific application of angle direction. I think that if you want to create a generic module (r.convert.aspect or r.convert.angle) for transforming angles, then North should mean North. If for a specific application North means a direction a force is coming from, then the use should take that into account. In your case the original map gives the angle the wind is coming _from_, then the output should (IMHO) do the same.<span class="HOEnZb"><font color="#888888"><br>
</font></span></blockquote><div><br>This would be of no use for me (or the user) if it doesn't match to the GRASS convention. So what I suppose I should do is to explain in the documentation that the input should be measured from SOUTH (0=SOUTH) clockwise. <br>
<br>Thanks!<br><br>Madi<br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><span class="HOEnZb"><font color="#888888">
<br>
Moritz<br>
</font></span></blockquote></div><br><br clear="all"><br>-- <br><span style="border-collapse:separate;font-family:'Times New Roman';border-spacing:0px;font-size:medium"><span style="font-family:arial;font-size:small"><div>
<font color="#666666">Margherita DI LEO </font></div><div><font color="#666666">Postdoctoral Researcher</font></div><div><font color="#666666"><br></font></div><div><font color="#666666">European Commission - DG JRC </font></div>
<div><font color="#666666">Institute for Environment and Sustainability (IES). Unit H03 – FRC</font></div><div><font color="#666666">Via Fermi, 2749</font></div><div><font color="#666666">I-21027 Ispra (VA) - Italy - TP 261</font></div>
<div><font color="#666666"> </font></div><div><font color="#666666">Tel. +39 0332 78 3600 </font></div><div><font color="#666666"><a href="mailto:margherita.di-leo@jrc.ec.europa.eu" target="_blank">margherita.di-leo@jrc.ec.europa.eu</a></font></div>
<div><font color="#666666"><br></font></div><div><font color="#666666">Disclaimer: The views expressed are purely those of the writer and may not in any circumstance be regarded as stating an official position of the European Commission.</font></div>
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