[gradsusr] Max Value

Tue Apr 19 21:31:41 EDT 2011

Andy,
If you have a CTL file or your data and would be willing to share I could
look through it and see what you might be doing wrong.  Since I don't use
OpenGrads it might be a difference between the regular Grads and OpenGrads,
but I don't know.  There is one line that makes a difference whether you're
using analysis data or model output of your own, so let me know what kind of
data you're using.

Jeff

On Tue, Apr 19, 2011 at 7:50 PM, Andrew Revering <andy at f5data.com> wrote:

>  Jeff,
>
>
>
> I appreciate all your help with this… every time I try one of these
> solutions it doesn’t work for me. I’m not sure what I’m doing wrong.
>
>
>
> For the short version, ymax always returns :
>
>
>
> 1,
>
>
>
> A few questions:
>
> -          Am I supposed to be using something like x=0,x=1078 (IE the
> dimensions of my image) or lon=-98,lon=-80 (the coordinates of the map
> edges?
>
> -          When in the script, do I need the ‘’ around the values?
> Likewise do I use ‘’ around my mapping variable?
>
> -          I’m using OpenGrads, I don’t know if that makes a difference.
>
> -          Where you have y1, y2, x1, x2, I’m replacing that with my
> actual values, correct? Or do I need to create those variables and populate
> those with my coordinates?
>
> -          I’m running a customized WRF-NMM, fyi.
>
>
>
> I tried the long version but had no success there either. When I tried to
> display the contents of max_locx and max_locy it simply displayed max_locx
> and max_locy. J Obviously I’m not doing something right. Must be a
> misunderstanding of the scripting language.
>
>
>
> Do you have a working script you could post that I could try to get to work
> with my CTL files. If I can get one that works (prints coordinates on an
> image) I can work backwards from there to see what I’m doing wrong.
>
>
>
> Thanks for your help.
>
> Andy
>
>
>
>
>
> *From:* gradsusr-bounces at gradsusr.org [mailto:
> gradsusr-bounces at gradsusr.org] *On Behalf Of *Jeffrey Duda
> *Sent:* Saturday, April 16, 2011 12:03 PM
> *To:* GrADS Users Forum
> *Subject:* Re: [gradsusr] Max Value
>
>
>
> Andrew,
>
> I made a script to do the same thing.  I've noticed in mine that I broke up
> your one line into two.  That might make the difference.  I think what is
> going on is the command is searching through your UNDEF values and finding
> those to be the max.  Here's how it goes in my code:
>
> 'define mxy = max('ans',x='x1',x='x2')'
> 'd maxloc(mxy,y='y1',y='y2')'
> ymax = subwrd(result,4)
>
> Attached is an image showing how it works.  The field is 850 mb theta-e.
> Script output is:
>
> The actual maximum location is at (x,y) = (223,36) or (lat,lon) =
> (36.0997,-97.4195) and is 340.864
> The actual minimum location is at (x,y) = (146,279) or (lat,lon) =
> (42.9153,-100.243) and is 310.718
>
> Before I learned the faster way of doing this, I made another script that
> does it using arrays.  It took a bit longer to run, but I never had a
> problem with accuracy.  It rejects candidates that are too high or too low.
> Here's the beef of that code:
>
> *Finding the location of maximum value
> max = -999999
> yy = y1
> while (yy <= y2)
>  'set y 'yy
>  'd maxloc('ans',x='x1',x='x2')'
>  line = sublin(result,2)
>  index = subwrd(line,4)
> * if (index < 1e+6 & index > -1e+6)*  (THIS TELLS THE SCRIPT TO REJECT A
> POINT IF IT ESSENTIALLY IS OFF THE GRID, I.E., AN UNDEF)
>   'set x 'index
>   'd 'ans
>   line = sublin(result,2)
>   act_max = subwrd(line,4)
> *setting index of max value into array
>   max.yy.1 = index
> *setting actual max value into array
>   max.yy.2 = act_max
>   'set x 'x1' 'x2
>   if (max.yy.2 > max)
>    max_val = max.yy.2
>    max_locx = max.yy.1
>    max_locy = yy
>    max = max_val
>   endif
>  endif
>  yy = yy + 1
> endwhile
>
> Let me know if you have further questions.
>
> Jeff Duda
>
> On Fri, Apr 15, 2011 at 5:53 PM, Andrew Revering <andy at f5data.com> wrote:
>
> I’m trying to do a max value plot… I got it to give me coordinates, but
> it’s not quite right. No matter what the variable is on the map that I’m
> trying to find the max value for, it always gives me coordinates (and plots
> visually) in the far lower left corner of the screen where there are no
> values.
>
>
>
> Here is my code:
>
>
>
>
>
> ‘d maxloc(max(tt,x=0,x=1028),y=0,y=768)’
>
> Line=sublin(result,2)
>
> Ygrd=subwrd(line,4)
>
> ‘d maxloc(max(tt,y=0,y=768),x=0,x=1028)’
>
> Line=sublin(result,2)
>
> Xgrd=subwrd(line,4)
>
>
>
> ‘set x ‘xgrd
>
> Lonval = subwrd(result,4)
>
>
>
> ‘set y ‘ygrd
>
> Latval = subwrd(result,4)
>
>
>
> ‘q w2xy ‘lonval’ ‘latval
>
> Xpos = subwrd(result,3)
>
> Ypos = subwrd(result,6)
>
>
>
> Then I go further to plot the coordinate, which works. The printed lat/lon
> is correct for where the marker is, but it is NOT where the max val is. Its
> way down in the lower left corner of the image.
>
>
>
>
>
>
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>
>
>
>
> --
> Jeff Duda
> Iowa State University
> Meteorology Graduate Student
> 3134 Agronomy Hall
> www.meteor.iastate.edu/~jdduda <http://www.meteor.iastate.edu/%7Ejdduda>
>
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>
>

-- 
Jeff Duda
Iowa State University
Meteorology Graduate Student
3134 Agronomy Hall
www.meteor.iastate.edu/~jdduda
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