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Re: IDL 8.2.2 released [message #83251 is a reply to message #83056] Wed, 13 February 2013 14:52 Go to previous messageGo to previous message
timothyja123 is currently offline  timothyja123
Messages: 57
Registered: February 2013
Member
On Wednesday, February 13, 2013 9:04:35 PM UTC+11, Fab wrote:
> Hi Timothy
>
>
>
>
>> I have been looking into your NetCDF suggestion.
>
>>
>
>> I have hit a problem however in that the IDL library
>
>> does not seem to have an option to compress the NetCDF files.
>
>
>
> Which version of IDL are you using? With 7.1.1 (patched for netCDF) and
>
> higher this should be no problem. But you have to specify that you want
>
> to use netCDF 4 when creating the file, with the /NETCDF4_FORMAT
>
> keyword: http://www.exelisvis.com/docs/NCDF_CREATE.html
>
>
>
> NetCDF4 allows you to create files larger than 2gb (upper limit for
>
> netCDF3 files) and also to use the three compression keywords when
>
> defining a variable (GZIP, CHUNCK_DIMENSIONS, SHUFFLE):
>
> http://www.exelisvis.com/docs/NCDF_VARDEF.html
>
>
>
> NetCDF is very fast, but the more you compress, the slowier it will be
>
> though. I found almost no win in file size when going from GZIP=5 to
>
> GZIP=9 so I suggest to stick by 5. I also noticed that creating
>
> compressed files takes longer but that reading them is almost as fast as
>
> uncompressed ones, but this should be tested in a proper benchmark. The
>
> compression will be very efficient if your data is very recurrent (many
>
> zeros for example).
>
>
>
> And again, I highly recommend David's NCDF_FILE object, which makes it
>
> much more fun to work with ncdf files and has no limitations (all
>
> keywords are accessible):
>
> http://www.idlcoyote.com/programs/ncdf_file__define.pro
>
> (the only drawback of David's tool is that it is "all objects" and
>
> therefore parsing a lot of files having a lot of variables/attributes is
>
> a bit slow)
>
>
>
> Cheers,
>
>
>
> Fab

Hi Fab,

Yes this works I didn't realise at first that compressing was done on a per variable bases. Thanks you for pointing that out. The new files definitely load much faster and also seem to compress slightly more which is another plus.
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