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Re: packing
- Subject: Re: packing
- Date: Tue, 15 Aug 1995 11:03:19 -0600
Hi Piotr,
> I am not sure if the previous mail got to you.
Apparently not, this is the first message I've seen from you recently.
> I am trying to save data from the Navy NOGAPS model
> which uses 5byte integer to write the data
Do you mean 5-byte or 5-digit? 5-byte integer data could store 2^40
different integer values, which would provide a precision of about 12
significant digits. I'll assume you mean 5-digit data, since you later say
> The ipack is written with
>
> format(120*i5)
which implies 5-digit data.
> unpack=ipack*fact+xmin
>
> where
>
> fact=(xmax-xmin)/99998.
>
>
...
>
> How should I go about it with NeCDF. Is it possible to write
> ipack array ? I would assume that many people ask the same question.
There are some common attribute conventions for packing floating-point data
into 8-bit or 16-bit integers, using the "scale_factor" and "add_offset"
attributes. Although these are described in the netCDF User's Guide under
the section on commonly used attributes, there is a better description in
the document available at the URL:
http://ferret.wrc.noaa.gov/noaa_coop/coop_cdf_profile.html
If more precision is required than 16-bits, the current version of netCDF
doesn't offer much help much. netCDF version 3.0 will include better
packing capabilities, approaches to which are described in the document
available at URL:
http://www.unidata.ucar.edu/packages/netcdf/packing.html
--Russ
______________________________________________________________________________
Russ Rew UCAR Unidata Program
address@hidden http://www.unidata.ucar.edu