Re: Using fill value

Gina,

You set _FillValue for the derivative snowdepth_minavg_meters, but
not for its precursors. Try adding this line immediately following
snowdepth2D = onedtond(...):

   snowdepth2D@_FillValue = -9. ; attach original missing value

After that, I think you can legally do the following, without any if
statement. NCL should do the right thing, leave the missing values
alone and not perform the division on them.

   snowdepth_minavg_meters(n,:,:) = (/ snowdepth2D / 100. /)

http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/NclExpressions.shtml#MissingValues

If that doesn't work, then divide and conquer. Insert
printVarSummary(...) after each definition or change to an array
variable, and find the first inconsistency in the name or value of
missing value related attributes. HTH.

Dave Allured
CU/CIRES Climate Diagnostics Center (CDC)
http://cires.colorado.edu/science/centers/cdc/
NOAA/ESRL/PSD, Climate Analysis Branch (CAB)
http://www.cdc.noaa.gov/

Gina Henderson 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 <http://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
> <http://snowdepth_minavg_meters.nc>") ; remove any pre-existing file
> ncdf = addfile("snowdepth_minavg_meters.nc
> <http://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
>
>
>
> ------------------------------------------------------------------------
>
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Received on Fri Nov 21 2008 - 17:38:39 MST