[gradsusr] If Statements and Drawing Variables

Tue Apr 18 18:14:05 EDT 2017

Jeff,

Thank you for the help! I got that working. So I've gotta a few different
fields that I am working with here. What I want to be able to do is after
performing the maskout()and const() on those fields, combine the resulting
index value from all fields into one image. So in other words, taking the
lowest in each field and outputting that as the final image.

I would image you could use the same process [ maskout) + const() ]but
wouldn't that require a variables? (And I can't draw variables)

Thank you!

--

Sincerely,

*Carter J. Humphreys*

*Developer*

Mods for GRX

carter.humphreys at mods-for-grx.com | Support Email: support at mods-for-grx.com |
Website: www.mods-for-grx.com

On Mon, Apr 17, 2017 at 10:50 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:

> Unfortunately you can't define plottable fields like that. You need to use
> a combination of maskout() and const() to get the desired field. Nesting of
> const((maskout)) usually gets you what you want. maskout() works like an if
> statement, filtering out values you don't want to plot based on an
> inequality. The way it works is maskout(field,mask), where field is the raw
> field you want to plot, and mask is an expression which may include other
> fields and/or constants. For example, if you wanted to just plot EHI where
> it was > 1, you could do 'd maskout(ehi,ehi-1)'. The result of maskout is a
> field plotted only where the mask expression is > 0 (might be >= 0, I
> forget, but if you're dealing with a continuous field, the end result is
> the same). Anywhere the mask field does not satisfy the equation, the raw
> field is treated like missing data. This is where const() comes in. You can
> nest maskout() within const() to tell grads what to do with the missing
> data (like the ELSE part of the if-else block). If you wanted to fill the
> rest of the EHI-masked field with 0s, for example, you could do 'd
> const(maskout(ehi,ehi-1),0,-u)', where the -u flag specifies const() to
> only apply the else value to undefined values (created by the maskout).
>
> While maskout works best for one-sided (i.e., semi-infinite) inequalities
> (e.g., x > 5 or x <= -10), you can use it for bounded inequalities as well
> using the absolute value function. You'll have to get a little clever with
> your masking expression, but some simple algebra will do it for you. You
> can also sum values and take an average (where the bounded inequality is
> valid, you'll sum the same field twice, so taking the average will restore
> the original values to the field. For example, for your first expression:
> 'd 0.5*(maskout(ehi,ehi-0.25)+maskout(ehi,0.5-ehi))' would plot a band of
> EHI values at grid points where 0.25 < EHI < 0.5. You could wrap this in a
> const() function to change those values to 1: 'd
> const(0.5*(maskout(ehi,ehi-0.25)+maskout(ehi,0.5-ehi)),1)'. You can then
> do that for all your bands. There will not be any overlap.
>
> Of course, that's a longhand way of doing it. You can also just use
> repeated multiplied instances of nested const(maskout()) functions to get
> the same result in one grand command, although it will be quite involved.
> I'll give you a start and leave you to figure the rest out:
>
> 'd const(const(maskout(ehi,0.125 - abs(ehi-0.375)),1),0,-u)...
> This first chunk gives your first condition where index would be set to 1.
> Use multiplication for the other terms.
>
> Good luck!
>
> Jeff Duda
>
>
> On Mon, Apr 17, 2017 at 4:59 PM, Carter Humphreys - Mods for GRX <
> carter.humphreys at mods-for-grx.com> wrote:
>
>> Hello,
>>
>> I'm fairly new to GrADS and am trying use a script to search through a
>> model product using if statements and assign a value to a certain range of
>> that product. (I.e. if temp is between 45 and 55, x = 2) I then try to have
>> GrADS draw that variable but all I end up with is a blank map.
>>
>> Any help would be appreciated, it's probably simple but I've been pretty
>> much lost after trying this for a few days now.
>>
>> My Script:
>>
>> 'clear'
>> 'set mpdset hires'
>> 'sdfopen http://nomads.ncep.noaa.gov/dods/nam/nam20170417/nam_12z'
>>
>> 'define ehi = (capesfc*hlcy1000_0m)/160000'
>> 'define index = 0'
>>
>> if (ehi>=0.25 & ehi<0.50)
>> index = 1
>> endif
>>
>> if (ehi>=0.50 & ehi<0.75)
>> index = 2
>> endif
>>
>> if (ehi>=0.75 & ehi<1.00)
>> index = 3
>> endif
>>
>> if (ehi>=1.00)
>> index = 4
>> endif
>>
>> 'set gxout shaded'
>>
>> 'd index'
>>
>> 'cbar'
>> 'draw title GrADS Script Test'
>> 'printim C:/GrADS/GrADS_script_test.png png white'
>>
>> --
>>
>> Sincerely,
>>
>> *Carter J. Humphreys*
>>
>> *Developer*
>>
>>
>> Mods for GRX
>>
>> carter.humphreys at mods-for-grx.com | Support Email:
>> support at mods-for-grx.com | Website: www.mods-for-grx.com
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>
>
> --
> Jeff Duda
> Post-doctoral research fellow
> University of Oklahoma School of Meteorology
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20170418/da0dc27a/attachment.html 