[gradsusr] If Statements and Drawing Variables

Thu Apr 20 17:53:19 EDT 2017

Hmmm, I don't know, that doesn't seem to produce the result I need.

So for example if I have constant A, constant B, and constant C defined. I
wanna to draw whichever constant has the lowest value. So if A=2, B=3, C=8)
I'd want the output to be constant A, or 2.

I don't know if that's possible or not.

--

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 Wed, Apr 19, 2017 at 4:23 AM, Becker, Bernd <
bernd.becker at metoffice.gov.uk> wrote:

> check this for something similar, ignore the odd bits:
>
>
>
>
>
> * drought duration
>
> dur=10
>
> dur=4
>
>
>
> * probability threshold
>
> thresh1=3
>
> thresh2=6
>
> *
>
> *  where flood forecast signal for 2 consecutive days is at least thresh
> percent (higher than  zero)
>
> *  where 2 consecutive days of rain > 5 mm/day are predicted.
>
> *
>
> 'define p=const(const(maskout(cdf ,cdf -'thresh1'),1),0,-u)'
>
> *
>
> *  where -no- drought forecast signal for dur consecutive days is at least
> thresh percent
>
> *  where dur consecutive days of no rain are -not- predicted.
>
> *
>
> 'define d=const(const(maskout(cdf.2(t='dur'),cdf.2(t='dur')-'
> thresh2'),1),0,-u)'
>
> *
>
> *  where rain    forecast  has positive tendency, is increasing with time
> from week1 to week 2.
>
> *  where more rain falls in forecast week 2 than in forecast week 1.
>
> *
>
> 'define i=const(const(maskout(prec.3(t=2    ),prec.3(t=13)-prec.3(t=
> 6)),1),0,-u)'
>
> *
>
> *  where rain    forecast  has positive tendency, is increasing with time
> from week2 to week 3&4.
>
> *  where more rain falls in forecast week 3&4 than in forecast week 2.
>
> *
>
> 'define j=const(const(maskout(prec.3(t=2    ),prec.3(t=20)-prec.3(t=13)),
> 1),0,-u)'
>
> * where tendency for rainfall during the fx period is positve
>
> 'define k=const(const(maskout(i              ,j-1
> ),0),1)'
>
> *
>
> *  where temperature    forecast  has positive tendency, is increasing
> with time from week1 to week 2.
>
> *  where temperature    in forecast week 2 is warmer than in forecast week
> 1.
>
> *
>
> 'define l=const(const(maskout(tmean.3(t=2    ),tmean.3(t=13)-tmean.3(t=
> 6)),1),0,-u)'
>
> 'define m=const(const(maskout(tmean.3(t=2
> ),tmean.3(t=20)-tmean.3(t=13)),1),0,-u)'
>
> 'define n=const(const(maskout(l              ,m-1
> ),0),1)'
>
> * apply only in temperate areas, where Tmean<14C
>
> tcut=14
>
> 'define n=const(const(maskout(tmean.3(t=2    ), tmean.3(t=2) -
> 'tcut'        ),0),1)'
>
>
>
> 'set grads off'
>
> 'set warn off'
>
> 'set datawarn off'
>
> 'set gxout grfill'
>
> 'set ccolor 10'
>
> 'set ccols 0 10 0 '
>
> 'set clevs   0  1 '
>
> 'set black -1 .00000001'
>
> 'd p*d*k*n'
>
>
>
> hth
>
> *From:* gradsusr-bounces at gradsusr.org [mailto:gradsusr-bounces@
> gradsusr.org] *On Behalf Of *Carter Humphreys - Mods for GRX
> *Sent:* 18 April 2017 23:14
> *To:* GrADS Users Forum; jeffduda319 at gmail.com
> *Subject:* Re: [gradsusr] If Statements and Drawing Variables
>
>
>
> 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
>
>
> _______________________________________________
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> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>
>
>
> --
>
> Jeff Duda
> Post-doctoral research fellow
> University of Oklahoma School of Meteorology
>
>
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>
>
>
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>
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