Hi there,
With netCDF-C now supporting HDF dynamic filters, the behaviour of nccopy has
slightly changed. In the past nccopy could be used to uncompress files
previously compressed with custom HDF dynamic filters. Nccopy used to read
<infile>, relying on HDF to invoke the decompression using the filter, and then
it would create a new netCDF file, <outfile>, uncompressed. In version 4.6.0,
nccopy also reads <infile> relying on HDF as before, but then writes the new
<outfile> applying the filter options defined in <infile>. I guess this is the
new default behaviour when not passing the -F argument .
Is there any option that can be passed in the -F argument to tell nccopy not to
apply any compression algorithm?
Thanks! and keep up the good work! Dynamic filter write support is a very hice
feature!
Here an example, with a sample.nc file previously compressed with a custom HDF
filter.
jrgu@linux-ozpe:~/FiltersTest/Test> ncdump -h -s sample.nc
netcdf sample {
dimensions:
number_of_columns = 30 ;
number_of_rows = 60 ;
variables:
short effective_radiance(number_of_rows, number_of_columns) ;
effective_radiance:_Storage = "chunked" ;
effective_radiance:_ChunkSizes = 60, 30 ;
effective_radiance:_Endianness = "little" ;
effective_radiance:_Filter = "56782,2,1,60,30,16,1,0,0,0,0,0,0,0" ; // filterID
+ filter options (cd values)
ubyte pixel_quality(number_of_rows, number_of_columns) ;
pixel_quality:_Storage = "chunked" ;
pixel_quality:_ChunkSizes = 60, 30 ;
pixel_quality:_Filter = "56782,1,1,60,30,8,1,0,0,0,0,0,0,0" ; // filterID +
filter options (cd values)
// global attributes:
:_SuperblockVersion = 2 ;
:_IsNetcdf4 = 1 ;
:_Format = "netCDF-4" ;
}
I have added some debugging messages to the custom HDF dynamic filter and
obtained the following when using nccopy:
* Nccopy in NetCDF-c 4.4 and 4.5: the decoding functionality in the filter is
invoked once for each variable when reading in_file:
jrgu@linux-ozpe:~/FiltersTest/Test> ../netcdf-c-4.5.0/ncdump/nccopy sample.nc
sample_nccopy45.nc
Deconding
CD VALUES 2, 1, 60, 30, 16, 1, 0, 0, 0, 0, ...
Components: 1, Lines: 60, Samples: 30
DataBytes: 2
Decompression successfull
Decode End: 3600
Deconding
CD VALUES 1, 1, 60, 30, 8, 1, 0, 0, 0, 0, ...
Components: 1, Lines: 60, Samples: 30
DataBytes: 1
Decompression successfull
Decode End: 1800
* Nccopy in NetCDF-c 4.6: the decoding functionality in the filter is invoked
once for each variable when reading in_file. The encoding functionality in the
filter is invoked once for each variable when writing out_file
jrgu@linux-ozpe:~/FiltersTest/Test> nccopy sample.nc sample_nccopy46.nc
Deconding
CD VALUES 2, 1, 60, 30, 16, 1, 0, 0, 0, 0, ...
Components: 1, Lines: 60, Samples: 30
DataBytes: 2
Decompression successfull
Decode End: 3600
Deconding
CD VALUES 1, 1, 60, 30, 8, 1, 0, 0, 0, 0, ...
Components: 1, Lines: 60, Samples: 30
DataBytes: 1
Decompression successfull
Decode End: 1800
Encoding
CD VALUES 2, 1, 60, 30, 2, 1, 60, 30, 16, 1, ...
Components: 1, Lines: 60, Samples: 30
DataBytes: 2
Pixel: 1800
ERROR: Error in jpeglsCompress: Parameter values are not supported by CharLS.
Compression failed
ERROR: Error during the JPEG-LS compression of the dataset.
Encode End -> Result: 0
Encoding
CD VALUES 1, 1, 60, 30, 1, 1, 60, 30, 8, 1
Components: 1, Lines: 60, Samples: 30
DataBytes: 1
Pixel: 1800
ERROR: Error in jpeglsCompress: Parameter values are not supported by CharLS.
Compression failed
ERROR: Error during the JPEG-LS compression of the dataset.
Encode End -> Result: 0
Cheers,
Joaquín
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