Re: [netcdfgroup] NetCDF-3 file format changes

• To: "Joe Sirott" <Joe.Sirott@xxxxxxxx>, <netcdfgroup@xxxxxxxxxxxxxxxx>
• Subject: Re: [netcdfgroup] NetCDF-3 file format changes
• From: "Mark Rivers" <rivers@xxxxxxxxxxxxxxxxx>
• Date: Tue, 26 Feb 2008 15:31:38 -0600

I think there is some way to extend it to at least 4GB-1.  IDL claims
that it uses netCDF 3.5, but it supports single variables up to 4GB.
Here is an example:


IDL commands to create a single variable that is almost 4GB and write it
to a netCDF file (write_tomo_volume is a routine I wrote that writes
netCDF files in IDL).  An IDL "int" is 16 bits (2 bytes):

IDL> vol = intarr(2000, 1024, 1024) 
IDL> write_tomo_volume, 'test.netcdf', vol

Look at the file in the Linux file system:

-rw-r--r--  1 tomo_user geocars 4194304428 2008-02-26 15:23 test.netcdf

Now read the file back in and check its size:
IDL> vol = read_tomo_volume, 'test.netcdf'
IDL> help, vol                            
VOL             INT       = Array[2000, 1024, 1024] 

Mark Rivers


> -----Original Message-----
> From: netcdfgroup-bounces@xxxxxxxxxxxxxxxx 
> [mailto:netcdfgroup-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Joe Sirott
> Sent: Tuesday, February 26, 2008 3:12 PM
> To: NetCDF Group mailing list (netcdfgroup@xxxxxxxxxxxxxxxx)
> Subject: [netcdfgroup] NetCDF-3 file format changes
> 
> Hi,
> 
> In the "classic" netCDF file format (netCDF-3), a variable without a 
> record dimension cannot be larger than 2GB. This limitation has been 
> giving me a lot of headaches lately. I know that netCDF-4 is 
> supposed to 
> solve this problem, but there are a number of reasons why netCDF-4 is 
> not a good option for me (no Java write support, for one).
> 
> I could be missing something, but it seems like a very small 
> change to 
> the netCDF-3 file format would solve this problem. The only 
> requirement 
> would  be changing the variable size info in the netCDF 
> header from a 32 
> bit to a 64 bit int (and, of course, updating the version info in the 
> header).
> 
> I'm guessing that I'm not the only netCDF user who has run into this 
> problem and who is also reluctant to move to netCDF-4. Any 
> possibility 
> that Unidata could make these changes?
> 
> Cheers,
> 
> Joe S.
> 
> 
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• References:
  • [netcdfgroup] NetCDF-3 file format changes
    • From: Joe Sirott