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Re: netcdf to ascii

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  • Subject: Re: netcdf to ascii
  • Date: Wed, 23 Feb 2005 16:48:14 -0700
>To: address@hidden
>From: address@hidden
>Subject: Re: 20050223: netcdf to ascii
>Organization: ORST
>Keywords: 200502232324.j1NNOAv2008915, short

Hi Nilesh,

>   I am writing a fortran program to convert netcdf data to ASCII.
> my netcdf description for olr
>         short olr(time, lat, lon) ;
>                 olr:long_name = "Daily OLR" ;
>                 olr:valid_range = 0.f, 500.f ;
>                 olr:actual_range = 64.75f, 344.5f ;
>                 olr:units = "W/m^2" ;
>                 olr:add_offset = 327.65f ;
>                 olr:scale_factor = 0.01f ;
>                 olr:missing_value = 32766s ;
>                 olr:var_desc = "Outgoing Longwave Radiation" ;
>                 olr:precision = 2s ;
>                 olr:dataset = "NOAA Interpolated OLR" ;
>                 olr:level_desc = "Other" ;
>                 olr:statistic = "Mean" ;
>                 olr:parent_stat = "Individual Obs" ;
> 
> So I should read the olr values as integer (is that right). What
> does the short mean? And also what does the precision = 2s
> mean. Because when i read i get -ve values for the olr, but the
> valid range is 0.0 - 500.0.

You can either read the olr values as integer, as real, or as double.
The netCDF library converts numeric values to the type you request.

"short" is the netCDF external (on disk) type for signed 16-bit
integers.

I'm not sure what "precision = 2s" means, maybe 2 significant digits?

Although the valid rnage is 0.0 to 500.0, you have to transform the
packed values using the add_offset and scale_factor to get the actual
values as floating point numbers, using the formula

   unpacked_value = add_offset + ((packed_value) * scale_factor)

So, for example, an olr value read in as 1000, would actually unpack
to the value
 
    327.65 + 1000. * 0.01

or 337.65, which to 2 significant figures would be 340.

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden          http://www.unidata.ucar.edu/staff/russ