[ncl-talk] Missing values are regridded?

[Jiang, Lifen]

Hi Mary,

Thanks for creating the script, but it showed error message when I ran it:

fatal:Could not open ($NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl)
fatal:error at line 5 in file regrid.ncl

Do you have any idea about this?

Thanks again,

Lifen

________________________________
From: Mary Haley [haley at ucar.edu]
Sent: Tuesday, February 17, 2015 2:52 PM
To: Jiang, Lifen
Cc: ncl-talk at ucar.edu
Subject: Re: [ncl-talk] Missing values are regridded?

Hi,

I'm not sure why the area_conserve_remap function is not working. However, the documentation for this function states:

   "Missing values, designated by the _FillValue attribute, are not allowed. If any missing
    values are encountered, the remap will not be performed for that grid."

I take this to mean that it should have returned *all* missing values, which apparently it didn't. I will file a ticket on this. I think, though, you cannot use this routine if you have missing values.

Meanwhile, you can try ESMF_regrid instead.  I've created a new script for you, based on your original script, that uses "bilinear", "conservative", and "nearest neighbor" methods for regridding.

You need to replace this code:

regrid = area_conserve_remap_Wrap(t&lon,t&lat,t,newlon,newlat,False)

with this code:

opt                = True
opt at DstGridLat     = newlat
opt at DstGridLon     = newlon
opt at ForceOverwrite = True
opt at InterpMethod   = "conserve"

regrid             = ESMF_regrid(t,opt)

​Please see the attached "regrid_and_plot.ncl" script, which uses ESMF_regrid for the three methods, and creates a panel plot.

​--Mary


On Tue, Feb 17, 2015 at 12:50 PM, Jiang, Lifen <lfjiang at ou.edu<mailto:lfjiang at ou.edu>> wrote:
Hello,

I am regridding "y" (lat, lon) to 1 degree grids. My codes always re-map the missing values as well (-999) as the printed min is -994.176, which should be a positive number.

My code is enclosed below and my data file is attached.

Could anybody help me to find why missing function doesn't work?

Thanks for your time!

Lifen

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"

begin
fili = "2000_MPI-ESM-MR.nc"
a = addfile (fili, "r")
t=a->y

t at _FillValue  = -999.0
t at missing_value = t at _FillValue

t = lonFlip(t)
printVarSummary(t)

newlat=fspan(-89.50,89.50,180)   ;create a sequence for the new values of lat
newlon=fspan(-179.5,179.5,360)   ;create a sequence for the new values of lon

newlat at units = "degrees_north"
newlon at units = "degrees_east"

regrid= area_conserve_remap_Wrap(t&lon,t&lat,t,newlon,newlat,False)
printVarSummary(regrid)
print("regrid:  min="+min(regrid)+"  max="+max(regrid))

filo = "Regrid."+fili
system("/bin/rm -f "+filo)
fout=addfile(filo,"c")
fout at creation_date = systemfunc("date")
fout at title="Regrid_1*1 of "+fili
fout->regrid=regrid
end





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