Re: [ferret_users] regridding transformation should reduce dimension . . .

["William S. Kessler" <william.s.kessler@xxxxxxxx>]

Hi Andrew, Ryo -

I don't think that was Ryo's question. 

What he wants is for a field defined by @loc (once it is evaluated from a 3-d field) to have the grid of a 2-d field.

Of course Ferret understands it as 2-d (thus it can be plotted with SHADE), but the variable Z10 retains its 3-d grid. He would like it to be 2-d so he can refer to Z10[k=1], and get the single-z-level field.

But I understand a definition like TEMP[Z=@LOC:10] to be comparable to TEMP[Z=400], namely it describes a 2-d field that can be SHADEd, but it remains part of a 3-d grid. 

I think it can be converted to 2-d with RESHAPE:

LET Z102D = RESHAPE(Z10,X[GX=TEMP]+Y[GX=TEMP])

(No time to test this!)

Billy

> On Dec 1, 2015, at 9:58 AM, Andrew Wittenberg - NOAA Federal <andrew.wittenberg@xxxxxxxx> wrote:
> 
> Hi Ryo,
> 
> Thanks for the clearly-stated question.  [All: this is a good example
> of how to ask a question so that it gets answered quickly.  In
> particular, Ryo provided a working example using one of Ferret's
> built-in datasets, e.g. levitus_climatology, coads_climatology, or
> monthly_navy_winds; and also pasted in the Ferret header, which shows
> what Ferret version he was using, just in case it turned out to be a
> bug.]
> 
> Note that Z=@LOC doesn't mean "search from top to bottom for 10 degC."
> Instead it means "search within the future evaluation context for 10
> degC."
> 
> So when you later specify z10[k=1], @LOC dutifully searches only over
> k=1; and since 10degC isn't found in the top level, it evaluates to
> "missing."
> 
> To insulate @LOC from future contexts, specify explicit z-limits:
> 
>  NOAA/PMEL TMAP
>  FERRET v6.951 (10/29/2015)
>  Linux 2.6.32-573.7.1.el6.x86_64 64-bit - 10/30/15
>  1-Dec-15 12:40
> 
> yes? use levitus_climatology
> yes? let z10 = temp[z=0:6000@LOC:10]
> yes? let below_z10 = z[g=temp] LT z10
> yes? shade/x=180 below_z10
> yes? shade/z=400 below_z10
> 
> The relevant documentation is:
> 
> http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/XPRESSIONS#_VPINDEXENTRY_528
> 
> See also the following answer in the Ferret email archives:
> 
> http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2006/msg00098.html
> 
> which was found by searching the email archives for "missing context".
> 
> Andrew
> 
> 
> On Tue, Dec 1, 2015 at 6:06 AM, Ryo Furue <furue@xxxxxxxxxx> wrote:
>> Hi Ferret users,
>> 
>> I'm sure there has been discussions about this issue and I searched
>> our email archive and found some threads that touch upon it, but
>> didn't find whether it's "solved" or not.
>> 
>> The problem is that @LOC (and perhaps other similar transformations)
>> doesn't properly "eliminate" the axis.  For a (x,y,z) temperature
>> field, say, you can find the depth of an isopycnal:
>> 
>>   yes? z10 = temp[z=@LOC:10]
>> 
>> but, "SHOW GRID z10", it still has more than one gridpoints.  Nevertheless,
>> 
>>    yes? fill z10[k=1]   !--> undefined field
>>    yes? fill z10           !--> works!
>> 
>> See a complete example below.  This behavior looks like a bug to me.
>> 
>> This matters.  I wanted to define a mask on the basis of this
>> variable, something like:
>> 
>>   yes? let below_z10 = if z[g=temp] lt z10 then 1
>> 
>> but this doesn't work because z10[k=1, 2, 3, . . .] are undefined!
>> 
>> My temporary solution is
>> 
>>   yes? let grid = x[gx=temp] + y[gy=temp]
>>   yes? let z10_squashed = reshape(z10,grid)
>>   yes? let below_z10 = if z[g=temp] lt z10_squashed then 1
>> 
>> But, I guess Ferret should do this reshaping for me with @LOC.
>> 
>> Regards,
>> 
>> Ryo
>> ----------------------------------------
>> $ ferret
>>  NOAA/PMEL TMAP
>>  FERRET v6.94
>>  Darwin 14.1.0 - 02/26/15
>>  1-Dec-15 19:36
>> 
>> yes? set data levitus_climatology
>> yes? let z10 = temp[z=@LOC:10]
>> yes? show grid z10
>>    GRID GMS1
>> name       axis              # pts   start                end
>> XAXLEVITR LONGITUDE          360mr   20.5E                19.5E(379.5)
>> YAXLEVITR LATITUDE           180 r   89.5S                89.5N
>> ZAXLEVITR DEPTH (m)           20 i-  0                    5000
>> normal    T
>> normal    E
>> normal    F
>> yes? list/x=180/y=0 z10[k=1]
>>             VARIABLE : TEMP[Z=@LOC:10]
>>             FILENAME : levitus_climatology.cdf
>>             FILEPATH : /usr/local/ferret/data/
>>             LONGITUDE: 179.5E
>>             LATITUDE : 0.5S
>>             DEPTH (m): 0 to 5
>>        ....
>> yes? list/x=180/y=0 z10
>>             VARIABLE : TEMP[Z=@LOC:10]
>>             FILENAME : levitus_climatology.cdf
>>             FILEPATH : /usr/local/ferret/data/
>>             LONGITUDE: 179.5E
>>             LATITUDE : 0.5S
>>             DEPTH (m): 0 to 5000
>>          371.7
>> !---- temporary solution ----
>> yes? let grid = x[gx=temp] + y[gy=temp]
>> yes? let z10_reshaped = reshape(z10, grid)
>> yes? show grid z10_reshaped
>>    GRID (G002)
>> name       axis              # pts   start                end
>> XAXLEVITR LONGITUDE          360mr   20.5E                19.5E(379.5)
>> YAXLEVITR LATITUDE           180 r   89.5S                89.5N
>> normal    Z
>> normal    T
>> normal    E
>> normal    F
>> yes? list/x=180/y=0 z10_reshaped[k=1]
>>             VARIABLE : RESHAPE(Z10, GRID)
>>             FILENAME : levitus_climatology.cdf
>>             FILEPATH : /usr/local/ferret/data/
>>             LONGITUDE: 179.5E
>>             LATITUDE : 0.5S
>>          371.7
>> yes? list/x=180/y=0 z10_reshaped
>>             VARIABLE : RESHAPE(Z10, GRID)
>>             FILENAME : levitus_climatology.cdf
>>             FILEPATH : /usr/local/ferret/data/
>>             LONGITUDE: 179.5E
>>             LATITUDE : 0.5S
>>          371.7
>> yes?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
William S. Kessler
NOAA / Pacific Marine Environmental Laboratory
7600 Sand Point Way NE
Seattle WA 98115 USA

william.s.kessler@xxxxxxxx
Tel: +1 206-526-6221
Fax: +1 206-526-6744
Web: http://faculty.washington.edu/kessler/