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#107: CF Data Model 1.7
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Reporter: markh | Owner: cf-conventions@…
Type: task | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords:
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Comment (by biard):
Replying to [comment:67 jonathan]:
> Dear Jim and Mark
>
> The text David and I proposed was
>
> The cell methods construct describes the methods by which the data
values of the field construct represent variation within their cells.
>
> and Jim proposes
>
> The cell methods construct describes the methods by which the data
values of the field construct are derived from a source measurement field
(which may or may not be represented by an existing field construct).
>
> With respect to the differences between these, I would comment:
>
> 1. CF doesn't only deal with measurements (which sounds like obs), so
I don't think the word "measurement" should appear.
>
> 2. I think "derived" is too general. The reason for writing
"variation" in our definition is because all of the cell methods do that,
by calculating a statistic from the variation, or by indicating it has no
relevant variation because it is a point (intensive) or a sum (extensive).
I think this needs to be indicated by the wording. "Derived" could mean
all sorts of mathematical operation which are not encompassed by
`cell_methods`.
>
> 3. I don't see the parenthesis as really necessary, and I'm not sure
it's true. The source field may never have existed. If it's a point or
sum, then probably there was no source field. This field is the data, and
`cell_methods` tells us something about what it means.
>
> Best wishes
>
> Jonathan
Jonathan,
I'm not overly concerned with the specific wording used. The thing I was
trying to get at was the question that the cell_methods attribute is
answering, which seems to me to be, "What algorithm did I apply to get
from a set of input values to the set of output values stored within this
variable?" If the cell_method is "point", then the algorithm is a null
transform. If the answer is sum, then there was a sum; if mean, an
average; etc. In some cases the input values are found in another
variable within the file. In other cases the input values are not found
within the file, and may not have been preserved anywhere.
Describing cell_methods in entirely self-referential terms comes across to
me as quite awkward, as you are trying to talk about an input-output
process without mentioning the input.
Grace and peace,
Jim
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Ticket URL: <http://kitt.llnl.gov/trac/ticket/107#comment:69>
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