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16 April 2024

Version 5.2.4 of the netCDF Operators (NCO) has been released. NCO is an Open Source package that consists of a dozen standalone, command-line programs that take netCDF files as input, then operate (e.g., derive new data, average, print, hyperslab, manipulate metadata) and output the results to screen or files in text, binary, or netCDF formats.

The NCO project is coordinated by Professor Charlie Zender of the Department of Earth System Science, University of California, Irvine. More information about the project, along with binary and source downloads, are available on the SourceForge project page.

From the release message:

Version 5.2.4 fully implements the CF lossy metadata convention for the three NCO internal quantization algorithms that are also in libnetCDF. It also improves ncclimo diagnostics. No major new features are implemented. Skip this release if these changes are not important to you.

New Features

All numeric operators now support --qnt as a synonym for --ppc. Previous one could only use --quantize as a synonym, and --qnt just seemed like it needed to be one too. The first three are the same:
```
ncks --ppc default=3 --ppc prs_sfc=5 in.nc out.nc # Granular Bitround
ncks --qnt default=3 --qnt prs_sfc=5 in.nc out.nc
ncks --quantize default=3 --quantize prs_sfc=5 in.nc out.nc
ncks --baa=8 --ppc default=12 --ppc prs_sfc=15 in.nc out.nc # Bitround
```
http://nco.sf.net/nco.html#qnt
http://nco.sf.net/nco.html#ppc
http://nco.sf.net/nco.html#quantize

All numeric operators now write CF-compliant metadata for quantization algorithms through the NCO internal algorithms. (Previously NCO wrote CF metadata only for quantization performed by the netCDF library.) NCO no longer writes the really long quantization metadata attributes such as QuantizeBitGroomNumberOfSignificantDigits. Note that libnetcdf still does write these attributes (prepended by an underscore) when its quantization functions are invoked.

% ncks -O -7 --baa=8 --qnt prs_sfc=6 --cmp='shf|zst' in.nc out.nc
% ncks -m -v prs_sfc,compression_info out.nc
netcdf foo2 {
dimensions:
lat = 2 ;
lon = 4 ;
time = UNLIMITED ; // (10 currently)

variables:
char compression_info ;
compression_info:family = "quantize" ;
compression_info:algorithm = "BitRound" ;
compression_info:implementation = "NCO version 5.2.4" ;

float prs_sfc(time,lat,lon) ;
prs_sfc:long_name = "Surface pressure" ;
prs_sfc:units = "pascal" ;
prs_sfc:lossy_compression = "compression_info" ;
prs_sfc:lossy_compression_nsb = 6 ;
} // group /

Additional details are available in the ChangeLog.

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