<div>Ivan,</div>
<div>I've tried to do this in the past and have encountered the same problem.� I have not yet found a solution to it.� You'd really need to do those calculations in a few DO loops (in FORTRAN or something like it) using an IF statement in the calculation.� Grads does not do that kind of thing unfortunately.� You might be able to use the maskout function, however, but that is just speculation.� Good luck.</div>
<div>�</div>
<div>Jeff Duda<br><br></div>
<div class="gmail_quote">On Sun, Feb 21, 2010 at 4:54 AM, Ivan Toman <span dir="ltr"><<a href="mailto:ivtoman@inet.hr">ivtoman@inet.hr</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Dear GrADS users,<br><br>I need some help with scripting. I have to calculate change in wind<br>direction in degrees between two different times. I do this this way:<br>
<br>'define hwd0 = 57.3*atan2(ugrd10m(t='i'),vgrd10m(t='j'))'<br>'define hwd1 = 57.3*atan2(ugrd10m(t='j'),vgrd10m(t='j'))'<br>'define hwdc = hwd0-hwd1'<br><br>where hwd0 is present wind direction, and hwd1 is wind direction in past time.<br>
<br>The problem arises when there is, for example, hwd0=10deg, hwd1=350deg, the<br>result of this equation is of course -340 degrees. This is not good, because<br>I have to get something like +20 degrees as result (by words: wind changed<br>
direction for 20 degrees to the right).<br><br>In fact, when wind is backing result should be negative value (from 0 to<br>-180), and when wind is veering the result must be positive value (from 0 to<br>180), and never < -180 or > 180 degrees.<br>
<br>I hope you got the point? Can somebody help me please here? I feel this is a<br>trivial problem but I'm stuck unfortunately. Thanks a lot.<br></blockquote></div><br><br clear="all"><br>-- <br>Jeff Duda<br>Iowa State University<br>
Meteorology Graduate Student<br>3134 Agronomy Hall<br><a href="http://www.meteor.iastate.edu/~jdduda">www.meteor.iastate.edu/~jdduda</a><br>