[gradsusr] If Statements for Gridded Model Data Open GrADS

[Stephen McMillan]

Hi Matt,

In addition to Bernd's suggestion, also check out the "if" function, which
should have come with your opengrads package as part of the following
extension function set:

http://opengrads.org/doc/udxt/libbjt/

The "if" function syntax:
*if*(*EXPR1,OP,EXPR2,TRUE_EXPR,FALSE_EXPR*)

This function compares *EXPR1* and *EXPR2*, where 5 arguments are expected.
if their relation is true, *TRUE_EXP* is returned, otherwise expression
*FALSE_EXPR* is returned.
*OP*

One of the following: ==, =, >, <, >=, <=, !=
*EXPR2, TRUE_EXPR, FALSE_EXPR*

These can be a expression, constant or -u.


I have found this function to be very useful and much easier to handle than
using maskout and const, although there are probably cases where the latter
is more appropriate or advisable.

Stephen McMillan

On Wed, Jun 22, 2016 at 9:24 AM, Baker, Matt (Quebec - Atlantic) <
matt.baker at amecfw.com> wrote:

> Hi all,
>
>
>
> I have a question regarding Open GrADS.
>
>
>
> I’m trying to use *if statements* for scalar model data (eg. GFS and NAM)
> over a grid and I’m wondering if it’s possible to do this. As an example,
> I’m using if statements for these parameters: surface based CAPE, LI, and
> 500 mb relative humidity to create an index to plot on a map. So far GrADS
> isn’t showing that this is working, however, I can plot the model data
> individually so I don’t think it’s a case of missing data.
>
>
>
> Here’s some of the code for the NAM model. Note that I define the variable
> NAMHail to equal 0 at the start of the function.
>
>
>
>    if (modelNumberNAM>0)
>
>         set_maps(_map,_hasNegativeNAM)
>
>         'set grads off'
>
>         'set grid off'
>
>         'set gxout contour'
>
>         'set ccolor 0'
>
>         'set clopts -1 1 0.15'
>
>         'set cint 1'
>
>         'set cthick 6'
>
>         'set clab on'
>
>         'set csmooth on'
>
>
>
>         'NAMcape = CAPEsfc.'modelNumberNAM
>
>         if (NAMcape > 1500 & NAMcape < 2200)
>
>             'NAMHail = NAMHail + 1'
>
>         endif
>
>         if (NAMcape > 2199 & NAMcape < 3100)
>
>             'NAMHail = NAMHail + 2'
>
>         endif
>
>         if (NAMcape > 3099)
>
>             'NAMHail = NAMHail + 3'
>
>         endif
>
>
>
>         'set lev 500'
>
>         'NAMrh500=RHprs.'modelNumberNAM
>
>         if (NAMrh500 < 35)
>
>             'NAMHail = NAMHail + 3'
>
>         endif
>
>         if (NAMrh500 > 35 & NAMrh500 < 44)
>
>             'NAMHail = NAMHail + 1'
>
>         endif
>
>
>
>     endif
>
>
>
>     'set gxout contour'
>
>     'set ccolor 0'
>
>     'set clopts -1 1 0.15'
>
>     'set cint 200'
>
>     'set cthick 6'
>
>     'set clab on'
>
>     'set csmooth on'
>
>
>
>     'd NAMcape'
>
>
>
> Thanks!
>
>
>
> *Matt Baker*
>
> Meteorologist, Met-Ocean Services, Amec Foster Wheeler Environment &
> Infrastructure
>
> 133 Crosbie Road, PO Box 13216, St. John’s, NL A1B 4A5, Canada
>
> *matt.baker at amecfw.com <matt.baker at amecfw.com>**­­*      amecfw.com
>
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