Hi Mark,
Volumes of documentation have been written about cell_methods that I
have not kept up with, so this response comes with implicit caveats.
Maybe this response is "coming from left field". But here goes ...
In your ensemble mean example (the second/result example on your Wiki)
the ensemble axis is no longer an axis of the variable sh_sd. The
ensemble mean operation is a uniform property over the entire domain of
the variable sh_sd, rather than a mean that was calculated over a unique
coordinate range represented by each cell of an axis. Rather than
using cell_methods, shouldn't the ensemble mean be documented through a
"history" variable, or some other machinery that describes the lineage
of calculations that went into creating this variable?
- Steve
P.S. In the result dataset, in which you have included all of the
ancillary variables that describe the ensemble (a nice touch), the
string "ensemble:mean" becomes a (potentially) nice, complete
description of the operation that has been performed -- clean and
self-describing.
================================================
On 10/25/2013 2:55 AM, Hedley, Mark wrote:
Hello CF
I am interested in defining cell methods where there are no coordinates.
I have a set of cases which I do not think fit the patterns in the
current conventions.
I suggest that we provide further capability for defining cell method
instances.
I have prepared a use case on the Trac wiki, to illustrate one of the
cases that is driving this:
https://cf-pcmdi.llnl.gov/trac/wiki/aggregateExampleMH
Am I right that there is not a currently available capability for
defining the result data set in this case?
I think this case and many others may be addressed by adding the
following text to the conventions document, appending to:
7.3.4. Cell methods when there are no coordinates
the text:
/
/
Where the cell method refers to a nominal cell, which is not described
by a data dimension, ancillary variables may be referenced by a cell
method to indicate the concepts the aggregation took place over.
To define this, the syntax:
"ancillary_variable_name_1: ancillary_variable_name_2: cell_method_name"
is used.
In this case, referenced ancillary variables may be extensive, with
multiple values, but they must be invariant with respect to the data
variable: they may share no data dimensions.
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