You should find a way to use the maskout function nested within the const function to do this. It's hard for me think of an exact way since your logical statement is compound in nature, but I can give you an example for a simple logical statement.<br>
<br>If you wanted only to mask out values where the terrain is < 2 km, you could use a command like<br>'define var = const(maskout(njet,thgt-2),-u,XX)', for thgt being the array storing terrain heights in meters and njet stores the number of jet occurrences.<br>
<br>This command would plot the number of jet occurrences, but in areas where the terrain height was < 2 km it would plot a constant value of XX, which can be whatever you want it to be. I would suggest making it a value that is not in the range of njet (so something either negative or very large, i.e., non-zero) so that you could make it show as a different color. Then, before plotting var, set a color table that includes the contour value you set in the definition.<br>
<br>For the other part of the logical statement, you could define a second field much like the first. Set the undefined value to something other than XX, but still negative or very large.<br>'define var2 = const(maskout(njet,njet),-u,YY)'<br>
<br>Finally, display your final field as 'd 0.5*(var+var2)'. I think Grads will take the union of the undefined areas and plot them both in the sum. The reason for the 0.5 factor is because you are double counting the number of jet occurrences otherwise. As far as the coloring goes, you'd have to set a final color table that includes contours for both XX/2, YY/2, and (XX+YY)/2 (since some grid points may be masked by both terrain and zero counts), as well as for the colors of the count occurrences.<br>
<br>Hopefully this helps. Mess around with this a little and see if you can get something that works.<br><br>Jeff Duda<br><br><div class="gmail_quote">On Wed, Jan 23, 2013 at 10:01 AM, Dana Doubler <span dir="ltr"><<a href="mailto:doublerd@msu.edu" target="_blank">doublerd@msu.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi there,<br>
<br>
We are preparing climatological maps of the frequency and<br>
characteristics of jet maxima from gridded data. On these maps we would<br>
like to "mask out" area with high elevations (>2 km) and also "mask out"<br>
areas were no jets were reported in our study period. We do not want<br>
the "0" or "missing value" indicators to be considered in the GrADS<br>
interpolation process. We are using the command "undef" to define a<br>
masking value. Ideally, however, we would like to show on the<br>
climatological maps the areas that have been masked due to high<br>
elevation in one color and the areas that have been masked because of no<br>
jet occurrences in another color. We haven't been able to figure out<br>
how to do this. Is this possible in GrADS? Thanks in advance for your<br>
help.<br>
<br>
Dana<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Jeff Duda<br>Graduate research assistant<br>University of Oklahoma School of Meteorology<br>Center for Analysis and Prediction of Storms<br>