Dear Vegard, all,
Please find enclosed the draft netCDF-U conventions, as presented to the Earth
System Science DWG at the last OGC TC Meeting in Bruxelles last wednesday.
We are continuing the discussion on the draft within the relevant OGC Working
Groups, to address and incorporate comments and improve the document for the
next Meeting (march 2012, Austin, Texas).
The contribution of the CF-metadata community would be very welcome.
To facilitate communication and avoid cross-posting, I would ask the interested
readers to contact me, so we can keep them posted (possibly we may set up a
dedicated mailing list, if need be).
As you will read in the attachment, we have tried to be convention-neutral, in
particular making sure that netCDF-U fully integrates with the netCDF-CF
Conventions, using the same constructs when possible (e.g. the
ancillary_variables attribute).
Ideally, we think of datasets that would conform to _both_ the conventions:
:Conventions = "CF-1.5 UW-1.0"
NetCDF-U is based on a generic mechanism for annotating netCDF variables
according to the UncertML conceptual model.
The rationale for this it that we argue a probabilistic description of
scientific quantities is a cross-cutting aspect that may be modularized.
In particular, we wouldn't "clutter" the application-level dictionaries with
probabilistic concepts and jargon.
This said, I think the cell-methods mechanism has a partial overlapping with
netCDF-U, in that it can account for (some of the) UncertML Summary Statistics
concepts. However, it does not currently address Distributions and Samples.
We could think of extending it, but we preferred to introduce a new mechanism,
based on the standard URI syntax and RDF semantics.
On the other hand, the cell-methods mechanism is arguably more fine-grained
than netCDF-U, allowing to express different methods on multi-dimensional
variables, particular as far as the semantics of dimension intervals is
concerned.
I am unclear at the moment how much this is application dependent, and hence
strictly pertaining to the CF conventions.
In other words, it may be that some application would still need the more
fine-grained semantics of CF cell-methods to make sense of the data.
This is in line with our aim of netCDF-U being complementary to netCDF-CF, and
not replacing it.
On the other hand, a generic mechanism for associating distinct summary
statistics semantics to distinct dimension variables may be useful in general.
We are looking forward to investigate this further and we welcome your
expression of interest in being involved in this discussion.
Regards,
LB
Il giorno 29/nov/2011, alle ore 10:17, Vegard Bønes ha scritto:
> Hi,
>
> Unfortunately, I did not see your email until today, so I have not taken it
> into consideration when choosing how to handle probabilities for myself.
>
> Like Roy, however, I believe that expressing probabilities as dimensions
> rather than attributes is the best approach for this.
>
> The problem with attributes is that if you have many variables and many
> probabilities or percentiles, you will get a huge amount of separate
> variables in your data set, and the relationship between them is not as easy
> to see as when (for example) all percentiles for air temperature are lumped
> into the same variable. If many users are like me, and use ncdump and ncview
> to look at the data, this will be a huge advantage.
>
>
> VG
>
>
> ----- Original Message -----
> Fra: "Lorenzo Bigagli" <[email protected]>
> Til: [email protected], "vegard bones" <[email protected]>
> Kopi: "Nativi Stefano" <[email protected]>
> Sendt: 24. november 2011 18:07:07
> Emne: [CF-metadata] standards for probabilities
>
>
> Dear Vegard, all,
>
>
> I take the opportunity to inform you that we are drafting a proposal for a
> netCDF convention on uncertainty (NetCDF-U).
> This work is partly developed in the framework of the FP7 UncertWeb project.
>
>
> We are going to present it next wednesday at the Open Geospatial Consortium
> TC Meeting in Bruxelles, to circulate it shortly after.
>
>
> We have tried to be convention-neutral, in particular making sure that
> netCDF-U fully integrates with the netCDF-CF Conventions, even using the same
> constructs when possible (e.g. the ancillary_variables attribute).
> Ideally, we think of datasets that would conform to both the conventions:
> :Conventions = "CF-1.5 UW-1.0"
>
>
>
>
> NetCDF-U is based on a generic mechanism for annotating netCDF variables
> according to the UncertML conceptual model.
> The first example in your use-case would read something like (note that CF
> attributes are unchanged):
>
>
> float precipitation_25(time, x, y) ;
> precipitation_25:standard_name = "precipitation_amount" ;
> precipitation_25:long_name = "precipitation_amount 25th percentile" ;
> precipitation_25:ref = " http://www.uncertml.org/statistics/percentile " ;
> precipitation_25:level = "25" ;
>
>
>
>
> The second, provided we have a variable "difference(Lat=100, Lon=100)" that
> contains the difference between the observed value and the forecast:
>
>
> float probability(Lat=100, Lon=100) ;
> probability:ref = " http://www.uncertml.org/statistics/probability " ;
> probability:gt = "-2.5" ;
> probability:lt = "2.5" ;
>
>
>
>
> I apologize if this is not clear enough, for the moment, and I hope it can be
> of prospective interest.
> Any comment is very appreciated.
>
>
> Best regards,
> Lorenzo Bigagli
>
>
>
>
>
>
>
>
> ---
> Dott. Lorenzo Bigagli
>
> Consiglio Nazionale delle Ricerche
> Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA)
>
>
> i: Area della Ricerca di Potenza, Contrada Santa Loja
> Zona Industriale, 85050 Tito Scalo (PZ), Italia
> t: +39 0971 427221
> f: +39 0971 427222
> m: [email protected]
> _______________________________________________
> CF-metadata mailing list
> [email protected]
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
_______________________________________________
CF-metadata mailing list
[email protected]
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
