Hello Vergand,
One of my jobs is running a parameter vocabulary that currently has over 27,000 entries. Much of its bulk is due to the assignment of multiple parameter names for each step in a numeric sequence - such as radiation wavelengths or sediment grain-size expressed as percentiles.
Consider a scenario where you start with a small group of standard percentiles - say 5, 25, 50, 75, 95. You set up a parameter name for each of these in the first instance, which is easy. Then along comes another user who wants to describe data with percentiles at a resolution of 1 per cent. So another 95 parameter names need to be set up. Then along comes another user who wants a resolution of 0.1 per cent. I start drowning in names and nobody can find anything.
However, had I followed Jonathan's second solution all I would need to do as a vocabulary manager is set up one concept to describe the percentile axis, which covers every user from those who use a handful of percentiles to those whose percentile resolution requirements are beyond the bounds of my imagination.
I know Jonathan's first option was based on propogation of cell methods and not standard names. However, these still need managing and if they become excessively abundant they also become difficult to navigate.
Cheers, Roy.
________________________________________
From: Vegard B?nes [vegard.bones at met.no]
Sent: 15 November 2011 13:17
To: Lowry, Roy K.
Cc: cf-metadata at cgd.ucar.edu; Jonathan Gregory
Subject: Re: [CF-metadata] standards for probabilities
Dear Roy,
Can you be a bit more concrete about why you prefer the second alternative?
-- Vegard
----- Original Message -----
Fra: "Roy K. Lowry" <rkl at bodc.ac.uk>
Til: "Jonathan Gregory" <j.m.gregory at reading.ac.uk>, "Vegard B??nes" <vegard.bones at met.no>
Kopi: cf-metadata at cgd.ucar.edu
Sendt: 15. november 2011 11:17:01
Emne: RE: [CF-metadata] standards for probabilities
Dear Jonathan,
I prefer your second alternative. It's not what I do, but it's what I wish I did!!
Cheers, Roy.
________________________________________
From: cf-metadata-bounces at cgd.ucar.edu [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory [j.m.gregory at reading.ac.uk]
Sent: 15 November 2011 10:11
To: Vegard B??nes
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] standards for probabilities
Dear Vegard
> I want to express such things as "25th percentile precipitation amount" (based on ensemble data), and probability that air temperature will be within 2.5 degrees of the forecast. How should I do this?
You are right, this case has not yet been dealt with, although the guidelines
for construction of standard names foresee that needs like this might arise!
If the quantity is a precipitation_amount, it's fine to use that standard
name. The question is how to record that is the 25th percentile. Two possible
ways to do this would be:
* To extend the possible syntax of cell_methods so that it can describe
percentiles. It is already possible to indicate a median in cell_methods, and
that is a particular percentile. The advantage of this way of doing it would
be that you would record whether the distribution of precipitation amounts
being considered was for time-variation, or spatial variation, or some other
kind of variation. Obviously you could have a probability distribution with
percentiles for many different independent variables.
* To use a size-1 or scalar coordinate variable to record the probability,
with a new standard_name, perhaps
cumulative_distribution_function_of_precipitation_amount.
The value of this coordinate would be 0.25 for the 25th percentile. The
advantage of this method would be that you could have several different
percentiles in the same variable, by having a multivalued probability coord.
If you wanted to be specific about what the independent variable was, that
would have to be included in the standard name as well e.g.
cumulative_distribution_function_of_precipitation_amount_over_time.
What do you think?
Cheers
Jonathan
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Received on Tue Nov 15 2011 - 06:35:59 GMT
