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[netCDF #ISA-863293]: Behaviour of nc_def_var_deflate



Hello Dinesh,

Currently, compression is passed to the 'zlib' library, which handles 
compression.  What sort of compression ratio are you getting?  It's entirely 
possible that the data you're working with does not lend itself to compression. 
 You might try writing a dataset of the same size using the same value for the 
variable across the grid.  This should lend itself very well to compression, 
and I would expect to see a better compression ratio.  It will certainly 
establish a 'best possible case' for what can be expected via compression. 

I hope this helps, have a great day!

-Ward

> Hi everyone,
> I am developing an application using NetCDF library to read/write NetCDF
> files. I am using version 4.3.3.1 of the library.
> 
> I am trying to understand how the NetCDF variables are being compressed.
> 
> I am creating a NetCDF4 file with a variable having dimensions 10000x20000
> and datatype uint16. This is about ~381 MB.
> 
> When I create the variable, I set the Deflate level to 5. So, when I write
> data to the entire variable, I expect the resulting file size to be much
> smaller than 381MB. However, this does not appear to be the case.
> 
> Am I missing something or is this because the data I am is not very
> correlated for the compression to do a good job?
> 
> Dinesh
> 
> 


Ticket Details
===================
Ticket ID: ISA-863293
Department: Support netCDF
Priority: Normal
Status: Closed
===================
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