This problem is already fixed for the next Netcdf release, according
to the tracker.
http://www.unidata.ucar.edu/support/help/MailArchives/netcdf/msg11533.html
https://bugtracking.unidata.ucar.edu/browse/NCF-213
--Dave
On Mon, Apr 8, 2013 at 1:16 PM, Heiko Klein <Heiko.Klein@xxxxxx> wrote:
> Hi,
>
> newer versions of netcdf (tested with 4.2.1 and 4.1.1) allow the generation
> of netcdf4 files with shuffling, chunking and compression by using the
> attributes:
>
> `_Format', `_Fletcher32, `_ChunkSizes', `_Endianness',_DeflateLevel',
> `_Shuffle', and `_Storage'.
>
> Unfortunately, these attributes are not only used for creating the file, but
> are also written as normal attributes to the file.
>
> A simple example:
>
> netcdf test {
> dimensions:
> time = UNLIMITED ; // (2 currently)
> variables:
> short time(time) ;
> time:_Storage = "chunked" ;
> time:_ChunkSizes = 1 ;
> time:_Shuffle = "true" ;
> time:_DeflateLevel = 3 ;
> // global attributes:
> :_Format = "netCDF-4 classic model" ;
> data:
> time = 12, 24 ;
> }
>
>
> looks after a 'ncgen -b', and 'ncdump -hs test.nc' like:
>
> netcdf test {
> dimensions:
> time = UNLIMITED ; // (2 currently)
> variables:
> short time(time) ;
> time:_ChunkSizes = 1 ;
> time:_DeflateLevel = 3 ;
> time:_Shuffle = "true" ;
> time:_Storage = "chunked" ;
> time:_ChunkSizes = 1 ;
> time:_DeflateLevel = 3 ;
> time:_Shuffle = "true" ;
> time:_Endianness = "little" ;
>
> // global attributes:
> :_Format = "netCDF-4 classic model" ;
> }
>
>
> When using some further processing, e.g. 'nccopy -k 3 -d 9 test.nc
> test9.nc', test9.nc will have ambiguos _DeflateLevel settings:
>
> $ ncdump -hs test9.nc
> netcdf test9 {
> dimensions:
> time = UNLIMITED ; // (2 currently)
> variables:
> short time(time) ;
> time:_ChunkSizes = 1 ;
> time:_DeflateLevel = 3 ;
> time:_Shuffle = "true" ;
> time:_Storage = "chunked" ;
> time:_ChunkSizes = 1 ;
> time:_DeflateLevel = 9 ;
> time:_Endianness = "little" ;
>
> // global attributes:
> :_Format = "netCDF-4" ;
> }
>
>
> I guess, all those _Attributes should never be written to the file by ncgen.
> (Tested with netcdf-4.2.1.1 on linux (ubuntu 12.04 64bit)).
>
> Regards,
>
> Heiko
>
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