The sentence in question is:
> "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 agree that the term "external values" would be ambiguous by itself. But
the sentance doesn't stop there. The phrase is immediately clarified by
stating that the external values are the ones in the netCDF file. I'm
having a hard time seeing what's ambiguous about that.
The use of "packed encoding" is not as precise as what's intended here.
Packing is only one application of scale_factor/add_offset. There are
others that don't involve reducing the data size.
Brian
On Fri, Oct 20, 2006 at 10:02:12AM -0700, Steve Hankin wrote:
> Jon,
>
> It certainly does look like the wording as-is (as you have quoted) is
> self-contradictory. But the phrase "units of the packed values", while
> intuitively clear, is actually a mis-statement, since "units" do not
> really apply to the packed data. The right wording is tough to find ....
>
> How about
>
> "When a variable uses a packed encoding (i.e. the variable has
> scale_factor and/or add_offset attributes -- see section 8.1)
> missing values are interpreted in the packed encoding. In other
> words, grid cells with missing values are detected before the data
> are unpacked."
>
> Not entirely happy with this, either ...
>
> - Steve
>
> =========================================
>
> John Caron wrote:
> >A user has misread section 2.5.1 on how missing values interact with
> >scale/offset, resulting in incorrectly written files. We might want to
> >consider some rewording on this in the future.
> >
> >Here is the relevent conversation:
> >
> >>>"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. "
> >>>
> >>>If I change this in my head to
> >>>
> >>>"The missing values of a packed variable are in the units of the
> >>>packed values, i.e., the values stored in the netCDF file."
> >
> >>I was confused by the "relative to the variable's external values".
> >>In my mind the "external values" are the ones that an external app
> >>sees, i.e. the unpacked values. Your interpretation makes perfect
> >>sense though.
> >
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>
> --
> --
>
> Steve Hankin, NOAA/PMEL -- Steven.C.Hankin at noaa.gov
> 7600 Sand Point Way NE, Seattle, WA 98115-0070
> ph. (206) 526-6080, FAX (206) 526-6744
>
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Received on Fri Oct 20 2006 - 11:41:06 BST
