Re: How to represent packed variable statistics (e.g., valid_range,

• Subject: Re: How to represent packed variable statistics (e.g., valid_range,
• From: Timothy Hume <tim.hume@xxxxxxxxxxxxxx>
• Date: Wed, 2 Oct 2002 20:23:21 +0000 (UTC)

Hi,

This discussion reminded me of how GRIB packs data. Ideally, it would be
nice for NetCDF to be able to handle data with an arbitrary number of
bits. Many meteorological data can be packed into only 9 or 10 bits (often
less), so packing them into 16 bit short integers is "wasteful". Aside
from that many satellite data are "naturally" 10 bit, and increasing them
to 16 bits can cause the file size to increase by tens of megabytes per
image.

By the way, does anyone know of software that can convert GRIB data to
COARDS or CF conventions? gribtonc converts GRIB to NUWG conventions?

Tim Hume

By the way, does anyone know of a GRIB to COARDS or CF

On Wed, 2 Oct 2002, Mark A Ohrenschall wrote:
> Hello,
>
> In the case of a packed variable (in which scale_factor and add_offset
> are used) both the COARDS and CF conventions indicate that missing_value
> and _FillValue should be likewise packed:
>
> COARDS: "In cases where the data variable is packed via the scale_value
> attribute this implies that the missing_value flag is likewise packed."
> CF: "The missing values of a variable with scale_factor and/or
> add_offset attributes (see section 8.1) are interpreted relative to the
> variable's external values, i.e., the values stored in the netCDF file."
>
> I'm assuming that for the sake of consistency, this means that all
> statistical variable attributes should be packed as well, e.g.,
> valid_range and actual_range, as well as mean and standard_deviation. Is
> this true?
>
> So for example, if I have real world data values for temperature between
> -1.6 and 31.4 and I'm applying a scale_factor of 0.1 then I would say
> the valid_range is -16, 314 and the mean is 116 (not 11.6)?
>
> Thanks,
>
> Mark
>
>

• Follow-Ups:
  • Packing and Grib to netCDF conversion
    • From: John Caron

• References:
  • How to represent packed variable statistics (e.g., valid_range, mean)?
    • From: Mark A Ohrenschall