Re: [netcdf-java] uv component data compression

Hi John and Lansing,

thank you for your replies, much appreciated. Indeed when I looked into the 
file I saw some jpeg2000 strings and the huge compression ration makes me think 
it is somehow a lossy compression (scaled/offset before sending to the 
compressor). I tried bzip2 and it does compress pretty well on the uv data, I 
get it down to ~540k compared to the original 400k of the grib file, this is 



 From: John Caron <caron@xxxxxxxxxxxxxxxx>
To: netcdf-java@xxxxxxxxxxxxxxxx 
Sent: Thursday, February 28, 2013 10:32 PM
Subject: Re: [netcdf-java] uv component data compression
Hi antonio:

Most grib data from ncep is scaled/offset to an integer and then jpeg000 
wavelet compressed. CDM can read but not write this format.

Your best bet is to get the floating point out of the CDM, subset just 
what you need, and compress it when sending to your client. Standard 
would be to decide how many bits of accuracy you need and convert to 
integers with that precision, then bzip2 or deflate.


On 1/30/2013 12:43 PM, Antonio Bleile wrote:
> Hi,
> I am currently trying to read the uv height over ground data of the GFS
> model, e.g. "gfs.t00z.master.grbf00.10m.uv.grib2". The file's size is
> roughly 400k. When I decompress the uv float arrays and save them as
> zipped files I get roughly a file of 1MB (uncompressed 2MB). I suspect
> the compressed grib data is somehow stored as 2 byte float perhaps? As
> I'm very unfamiliar with the netcdf library I'd like to learn more about
> how the data is compressed and decompressed within the grib file. The
> motivation of all this is that I'd like to display the UV data on an
> android device (which has insufficient resources to run netcdf library!)
> so I need to convert the grib compressed data into something more simple
> but yet efficiently compressed! I'd appreciate any pointers to the right
> documentation or any hints on how the uv data is compressed....
> Regards,
>    Antonio
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