Dear Charlie,
I for one have no objection, in general, to new cell methods - I don't
think that there are enough.
Your suggestions (mabs/mibs/mebs) are clearly well defined, though I'm
personally not so keen on the use of abbreviations. I've not seen
these terms before, and wouldn't have guessed what they all mean. This
is contrary to all of the other cell methods, which are unabbreviated
and, I suspect, nearly universally understood.
I dislike typing as much as anyone, but spelling them out is only 1 to
4 characters more than typing standard_deviation, the current longest
method name:
standard_deviation
mean_absolute_value
minimum_absolute_value
maximum_absolute_value
These terms seem nicely self describing to me. Do you think this is an
option?
There appears to be an error in the draft 1.7 document. The sentence
describing Appendix E (the cell-methods appendix) says "In the Units
column, u indicates the units of the physical quantity before the
method is applied." Actually the units column entries are valid
_after_ the method is applied. Variance is the only method for which
this currently matters. This can be addressed independently of the
rest of the cell_methods suggestions proposed here.
I think that this is OK. The column contains units after the method is
applied, defined in terms of the original units ('u'). However, I
agree that the terse description can mislead (as it did me just
now!). How about replacing:
"In the Units column, 'u' indicates the units of the physical
quantity before the method is applied."
with something like:
"The Units column contains the units of the physical quantity after
the method is applied, in terms of 'u', the units before the method
is applied."
All the best,
David
---- Original message from Charlie Zender (11AM 19 Feb 15)
Date: Thu, 19 Feb 2015 11:56:22 -0800
From: Charlie Zender <[email protected]>
To: CF Metadata Mail List <[email protected]>
Subject: [CF-metadata] New cell_methods: mabs/mibs/mebs?
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0)
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Dear CF-ers,
The statistics mabs/mibs/mebs stand for "Maximum absolute value",
"Minimum absolute value", and "Mean absolute value", respectively.
They are similar to max/min/mean statistics, and they can be useful
in characterizing data when one wants positive-definite metrics.
mebs (unlike mean) does not allow positive and negative values to
compensate eachother. Unlike rms, mebs not does weight outliers
quadratically. NCO (version 4.4.8) implements mabs/mibs/mebs as
fundamental statistics (like max/min/mean/rms), and annotates the
cell_methods attribute of variables reduced by these statistics with
the strings "maximum_absolute_value", "minimum_absolute_value", and
"mean_absolute_value". I suggest CF adopt this, or some variant
pursuant to discussion.
So I guess this is a request for discussion.
The relevant portions of CF are
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/cf-conventions.html#cell-methods
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/cf-conventions.html#appendix-cell-methods
The modifications that would be needed seem straightforward:
mention mabs/mebs/mibs in the text and then enlarge the existing
cell_methods table table by three rows.
There appears to be an error in the draft 1.7 document. The sentence
describing Appendix E (the cell-methods appendix) says "In the Units
column, u indicates the units of the physical quantity before the
method is applied." Actually the units column entries are valid
_after_ the method is applied. Variance is the only method for which
this currently matters. This can be addressed independently
of the rest of the cell_methods suggestions proposed here.
I think that this is OK. The column contains units after the method is
applied, defined in terms of the original units ('u'). However, the
terse description is misleading on first reading. How about something
like:
"In the Units column are the units of the physical quantity after the
method is applied, in terms of 'u', the units before the method is
applied."
Best,
Charlie
--
Charlie Zender, Earth System Sci. & Computer Sci.
University of California, Irvine 949-891-2429 )'(
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--
David Hassell
National Centre for Atmospheric Science (NCAS)
Department of Meteorology, University of Reading,
Earley Gate, PO Box 243,
Reading RG6 6BB, U.K.
Tel : +44 118 3785613
E-mail: [email protected]
