Re: Using fill value

Hi there,

also just to add, is there any way when I apply my land mask that the masked
gridpoints can be set to the missing value also? As presently they are set
to - in my output .nc file.

Thanks, Gina.

On Fri, Nov 21, 2008 at 5:32 PM, Gina Henderson <ginah_at_udel.edu> wrote:

> Hi all,
>
> I am trying to read data from an ascii file and set a missing value code of
> -9. However no matter what I set the _FillValue to be it just comes out as
> -999 and doesn't register in my output .nc file. I need the missing value
> set as I am performing an if test in a later program and ncl won't let me do
> an if on data without a missing value code.
>
> Also, I am trying to use an if statement to convert a value from cm to m if
> there is no missing data only and cannot seem to get it to work.
>
> Any tips on using this function or the if statement?
> Thanks, Gina.
>
> ; Load some resources
> 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/shea_util.ncl"
>
> begin
> ;
> ; Read the ascii file.
> ;
> ; Read in the data as an nlat*nlon x14 array
>
> nlat = 64
> nlon = 128
>
> snow_data=asciiread("minavg_t42.txt",(/nlat*nlon,14/),"float")
>
> ; Extract the lat coordinates from the data array.
> ; Since the latitude values are repeated, we only need to
> ; grab every nlon-th value.
>
> lat1d = snow_data(::nlon,0)
> lat1d_at_units = "degrees_north"
>
> ; Same for lon
>
> lon1d = snow_data(0:nlon-1,1)
> lon1d_at_units = "degrees_east"
>
> ; Define new variable for snow depth for all 12 months
>
> snowdepth_minavg_meters = new((/12,64,128/), float)
> snowdepth_minavg_meters!0 = "time"
> snowdepth_minavg_meters!1 = "lat"
> snowdepth_minavg_meters!2 = "lon"
>
> time = (/1,2,3,4,5,6,7,8,9,10,11,12/)
> snowdepth_minavg_meters&time = time
> snowdepth_minavg_meters&lat = lat1d
> snowdepth_minavg_meters&lon = lon1d
> snowdepth_minavg_meters&lat_at_units = "degrees_north"
> snowdepth_minavg_meters&lon_at_units = "degrees_east"
> snowdepth_minavg_meters@_FillValue = -9.
>
> ; set attributes
> snowdepth_minavg_meters_at_long_name = "snow depth"
> snowdepth_minavg_meters_at_units = "cm"
>
>
> do n=0,11
>
> ; Convert data to a 2D grid 64x128
>
> snowdepth1D = snow_data(:,n+2) ; first create 1D array
> snowdepth2D = onedtond(snowdepth1D,(/nlat,nlon/)) ; convert to 2D
>
> ; Assign named dimensions
>
> snowdepth2D!0 = "lat"
> snowdepth2D!1 = "lon"
>
> ; Assign coordinate variables
>
> snowdepth2D&lat = lat1d
> snowdepth2D&lon = lon1d
>
> ; Write snow data to new array containing all months and change value
> ; to meters except for missing values which are -9.0
>
> snowdepth_minavg_meters(n,:,:) = snowdepth2D
> if ((snowdepth_minavg_meters(n,:,:) .ne. snowdepth_minavg_meters@_FillValue))
> then
> snowdepth_minavg_meters(n,:,:) = snowdepth_minavg_meters(n,:,:) / 100.
> end if
>
> end do
>
> printVarSummary(snowdepth_minavg_meters)
>
> ; Mask out over ocean
> a = addfile("landmask.nc","r")
> clm_t42 = a->landmask
>
> snowdepthms_minavg_meters = snowdepth_minavg_meters
>
> ; Mask out all ocean points from t42
> snowdepthms_minavg_meters =
> mask(snowdepth_minavg_meters,clm_t42.eq.0,False)
>
> printVarSummary(snowdepthms_minavg_meters)
>
> ;=====================================================================
> ; Write data to new netcdf file
> ;=====================================================================
> system("/bin/rm -f snowdepth_minavg_meters.nc") ; remove any
> pre-existing file
> ncdf = addfile("snowdepth_minavg_meters.nc" ,"c") ; open output
> netCDF file
>
> ; make time and UNLIMITED dimension ; recommended for most
> applications
> filedimdef(ncdf,"time",-1,True)
>
> ; output variables directly
> ncdf->snowdepthms_minavg_meters = snowdepthms_minavg_meters ;
> write file
>
>
>

-- 
Gina Henderson
Graduate Student
Department of Geography
215 Pearson Hall
University of Delaware
Newark DE
19718-2541
Email: ginah_at_udel.edu
Ph: 302-831-2344

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Received on Fri Nov 21 2008 - 16:19:22 MST