[netcdfgroup] NCO is treating zero and NaN the same?

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• Subject: [netcdfgroup] NCO is treating zero and NaN the same?
• From: "Pan, Jianfu (GSFC-610.2)[ADNET SYSTEMS INC]" <jianfu.pan-1@xxxxxxxx>
• Date: Mon, 2 Dec 2013 17:56:52 +0000

I have a netCDF variable that has _FillValue attribute set to NaN (undefined 
value from, for example, dividing a number by 0).  When I tried to set it to a 
numeric value using ncatted, it changes all zeroes in data to the fill value as 
well in the process.  Is this a bug is there a way to retain the zero values 
while resetting the NaN fillvalue?

The following is the dump of a sample file I used. Both 0 and NaN in data 
become fill value (-999.) while I was expecting the zeros to remain.  The 
command I used to set fillvalue is:  ncatted -a "_FillValue,A,o,d,-999." nan.nc

******** Start of nan.nc dump ********
netcdf nan {
dimensions:
        latitude = 3 ;
        longitude = 3 ;
variables:
        double A(latitude, longitude) ;
                A:_FillValue = NaN ;
                A:long_name = "A Variable" ;
                A:units = "mm" ;
        double longitude(longitude) ;
                longitude:long_name = "longitude" ;
                longitude:standard_name = "longitude" ;
                longitude:units = "degrees_east" ;
        double latitude(latitude) ;
                latitude:long_name = "latitude" ;
                latitude:standard_name = "latitude" ;
                latitude:units = "degrees_north" ;

// global attributes:
                :Conventions = "CF-1.4" ;
data:

A =
  0.02, 0, NaN,
  0.3, 0.4, 0.5,
  0, 0.6, 0.8 ;

longitude = -80, -79, -78 ;

latitude = 10, 11, 12 ;
}
******** End of nan.nc dump ********

Thanks.

Jianfu Pan