Mark,
It seems to me that we have quite a few examples of coordinate variables
that have extra attributes that further define the contents. Time
coordinate variables, for example, have the calendar attribute. There
are many standard names that direct the developer to specify an
attribute (most always comment or flag_values/flag_meanings attributes)
that further defines the contents. Any variable can validly have
attributes associated with it.
If having a specific attribute name that's not mentioned in the CF
Conventions document called for in a standard name definition is too
troubling, the standard name definition could call for putting a string
of the form 'ensemble size N' in a comment attribute. Or it could call
for putting the ensemble size in a comment section in the cell_methods
attribute on the data variable as Jonathan and Karl's suggested.
Jonathan and Karl's suggestions imply a change to the conventions, since
they propose new standardized cell method comment names.
In all of these cases the information will be available to a human who
reads a file dump, but none of them make the information immediately
available to software automation. The addition to the cell_methods
attribute grammar is likely the least intrusive way to make it something
that people can write general software for. The down side to this
approach is that the information is not held with the coordinate
variable, which is the most natural place for it.
Another alternative is to add a new section to Chapter 5 that defines an
ensemble or sample pool coordinate type (or whatever name you prefer).
It may be worth the extra trouble to go ahead and give it formal
recognition instead of trying to work it into existing forms that, in my
opinion, don't fit it too well. I appreciate the desire to find the
least intrusive way to modify the conventions, but we can end up
painting ourselves into corners in the process.
Grace and peace,
Jim
On 7/29/15 3:24 AM, Hedley, Mark wrote:
> Hello Jim
>
> this is a really neat alternative approach
>
> I agree that the information about the ensemble_size is closely
> related to the realization coordinate and less closely related to the
> data variable, so this method encapsulates the metadata nicely.
>
> Whilst the solution is elegant, I cannot see a previous example of a
> coordinate variable within CF defining extra attributes, so I'm a bit
> wary that this approach will require a change to the conventions
> document, not just a new standard_name.
>
> Is there a neat way to use CF to provide metadata about a coordinate,
> rather than about a data variable?
>
> I think it's well worth considering, but it may be a path of some
> resistance
>
> many thanks
> mark
>
> ------------------------------------------------------------------------
> *From:* CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of
> Jim Biard [jbiard at cicsnc.org]
> *Sent:* 23 July 2015 13:11
> *To:* cf-metadata at cgd.ucar.edu
> *Subject:* Re: [CF-metadata] original_ensemble_size
>
> Hi.
>
> It seems to me that you would want a coordinate variable with the
> standard name 'realization' (whether scalar or multi-valued) and give
> it an attribute with the name 'ensemble_size'. You can store the
> realization number in the variable and the ensemble size in the attribute.
>
> Grace and peace,
>
> Jim
>
> On 7/23/15 6:11 AM, Hedley, Mark wrote:
>> I use the
>> 'coordinates'
>> attribute on my data variable, referencing the scalar 'ensemble_size'
>> variable, thus defining this ensemble_size as a scalar coordinate
>> variable for the temperature dataset
>>
>> mark
>>
>> ------------------------------------------------------------------------
>> *From:* CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of
>> Karl Taylor [taylor13 at llnl.gov]
>> *Sent:* 22 July 2015 22:53
>> *Cc:* CF Metadata List
>> *Subject:* Re: [CF-metadata] original_ensemble_size
>>
>> Hi all,
>>
>> I'm still curious about something:
>>
>> Suppose we have the temperature field stored from one member of an
>> ensemble of size 10. We want to make the size of the ensemble known
>> to the user. We store 10 as a scalar variable with standard name
>> "ensemble_size", but how does that scalar get associated with our
>> temperature variable (other than it having being stored in the same
>> file)?
>>
>> cheers,
>> Karl
>>
>> On 7/22/15 1:59 AM, Hedley, Mark wrote:
>>> Hello John, Karl et al
>>>
>>> I'm not sure I agree with John's last statement. I think that an
>>> ensemble is a defined collection of members, so my need is the need
>>> for ensemble size to be defined explicitly.
>>> The distinction that not all members may be present characterises
>>> the need for this metadata descriptor, rather than just using the
>>> dimension size of realization, which does not meet my requirement.
>>>
>>> On reflection, I think that I prefer Karl's name of 'ensemble_size'
>>>
>>> To restate my use case, I have a data set from an ensemble, where
>>> there is a coordinate variable called 'realization'. Let's say
>>> there are 23 members, this dimension is size 23.
>>>
>>> I want to reference the number of members in the ensemble, whilst
>>> sub-setting the data variable in various ways.
>>>
>>> The suggestion is to add a scalar coordinate to my original dataset,
>>> which contains the number of members in the ensemble. Then any
>>> sub-setting operation will retain this coordinate, and I will always
>>> be able to state that this member is member 0 of 23, 5 of 23 etc
>>>
>>> One requirement I have is to slice this variable, to result in a 2D
>>> data array, 2 1D coordinate variables: latitude and longitude; with
>>> all other coordinates as scalars.
>>>
>>> If it is reasonable to talk about an ensemble as a defined
>>> collection of members, then I agree with Karl, that a standard_name
>>> of 'ensemble_size' fits the bill. The description fits my use case
>>> nicely
>>>
>>> many thanks
>>> mark
>>>
>>>
>>> ------------------------------------------------------------------------
>>> *From:* CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of
>>> John Graybeal [jbgraybeal at mindspring.com]
>>> *Sent:* 22 July 2015 05:52
>>> *To:* Karl Taylor
>>> *Cc:* CF Metadata List
>>> *Subject:* Re: [CF-metadata] original_ensemble_size
>>>
>>> Karl,
>>>
>>> To my understanding (then and now), the use case is explicitly not
>>> what your definition describes. The entire point of the request was
>>> to provide a label that was clearly distinguished from the typical
>>> concept of ensemble size.
>>>
>>> John
>>>
>>>
>>>
>>> On Jul 21, 2015, at 16:36, Karl Taylor <taylor13 at llnl.gov
>>> <mailto:taylor13 at llnl.gov>> wrote:
>>>
>>>> Dear all,
>>>>
>>>> I wonder if the following might also meet requirements of the use case:
>>>>
>>>> name: *ensemble_size*
>>>> *
>>>> *
>>>> description: The number of member realizations in an ensemble.
>>>> This name provides context for any specific realization, which
>>>> might not be co-located with the other members of the ensemble.
>>>>
>>>> Karl
>>>>
>>>> On 7/20/15 9:49 PM, John Graybeal wrote:
>>>>> To save others the lookup, the use case phrasing that Mark signed
>>>>> on to were these words: "In my use case, the whole ensemble is not
>>>>> present, I only have a subset of the members. I have a metadata
>>>>> element telling me how many members there were at the time the
>>>>> ensemble was created, which I would like to encode." The entire
>>>>> thread is titled 'realization | x of n', but it is pretty, umm,
>>>>> rich with detail.
>>>>>
>>>>> The last email before discussion went silent appears to be mine:
>>>>>
>>>>>> Modified to fit Mark's use case, I think suitable text is:
>>>>>>
>>>>>> name: *original_ensemble_size*
>>>>>> *
>>>>>> *
>>>>>> description: The number of member realizations in the originally
>>>>>> constituted ensemble. This provides context for any specific
>>>>>> realization, for example orienting a member relative to its
>>>>>> original group (even if the group is no longer intact).
>>>>>>
>>>>>> This does not mention forecasting, preserves the origination
>>>>>> concept, and gives a bit of context, without constraining the
>>>>>> application. It could even be an ensemble of observations, or cat
>>>>>> videos, or ... you get the idea.
>>>>>
>>>>> I will let someone else provide the example of how that is
>>>>> associated with the variable, it will be more authoritative!
>>>>>
>>>>> John
>>>>>
>>>>>
>>>>> On Jul 20, 2015, at 14:42, Karl Taylor <taylor13 at llnl.gov
>>>>> <mailto:taylor13 at llnl.gov>> wrote:
>>>>>
>>>>>> Hi Mark,
>>>>>>
>>>>>> I didn't quite understand how the standard name gets associated
>>>>>> with a variable (containing 1 or more realizations from the
>>>>>> ensemble). Someone said it was through a scalar coordinate
>>>>>> variable, but I don't see how the ensemble member is a function
>>>>>> of the ensemble size, so why would this be appropriate?
>>>>>>
>>>>>> Could you supply an example?
>>>>>>
>>>>>> Also, I didn't follow why "original" was included in "original
>>>>>> ensemble size". Surely, you wouldn't report this number unless
>>>>>> you thought the ensemble size was pretty much set and wouldn't
>>>>>> change. In that case there shouldn't be a need for a "modified
>>>>>> ensemble size", so wouldn't "ensemble size" suffice?
>>>>>>
>>>>>> thanks,
>>>>>> Karl
>>>>>>
>>>>>>
>>>>>> On 7/20/15 9:24 AM, Hedley, Mark wrote:
>>>>>>> Hello CF
>>>>>>>
>>>>>>> Late last year we had a discussion about storing
>>>>>>> original_ensemble_size
>>>>>>> in a CF file
>>>>>>> http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2014/thread.html#57756
>>>>>>>
>>>>>>> There were a few options discussed, with John Graybeal making
>>>>>>> the suggestion
>>>>>>> original_ensemble_size
>>>>>>> /description: The number of members constituting an ensemble./
>>>>>>> for a new standard_name definition, which seemed to fit the case
>>>>>>> very well
>>>>>>>
>>>>>>> It does not seem to have been adopted into the standard names
>>>>>>> list as yet.
>>>>>>>
>>>>>>> Please may this name and definition be adopted, or reasons not
>>>>>>> to detailed here?
>>>>>>>
>>>>>>> thank you
>>>>>>> mark
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> CF-metadata mailing list
>>>>>>> CF-metadata at cgd.ucar.edu
>>>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>>>>
>>>>>> _______________________________________________
>>>>>> CF-metadata mailing list
>>>>>> CF-metadata at cgd.ucar.edu <mailto:CF-metadata at cgd.ucar.edu>
>>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>>>
>>>>
>>>
>>
>>
>>
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
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/formerly NOAA?s National Climatic Data Center/
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Received on Wed Jul 29 2015 - 09:02:58 BST
