Thanks, Jim.
Glad that my edit "find" skills haven't deteriorated too much.
best,
Karl
On 12/22/15 9:10 AM, Jim Biard wrote:
> Karl,
>
> This is not in CF. There is a statement that many assume that bounds
> are at the midpoints between coordinate values, but it then points out
> that this is not a convention. That's as close as it gets. If it was
> there in the past it is gone now.
>
> Grace and peace,
>
> Jim
>
> On 12/22/15 12:07 PM, Karl Taylor wrote:
>> Hi John,
>>
>> this is a bit of a tangent, but you state:
>> "Another possible use case is to represent contiguous bounds, where
>> lower_bounds(i+1) == upper_bounds(i), then one only needs n+1 values
>> instead of 2*n."
>>
>> I seem to recall this option in CF, but recently I was reviewing the
>> bounds specification, and I can't see where this is allowed. Was it
>> in the original standard and subsequently removed? Or am I just
>> unable to fine where it says you don't need the 2nd dimension on
>> bounds in this case?
>>
>> best regards,
>> Karl
>>
>> On 12/22/15 8:39 AM, John Caron wrote:
>>> Hi David:
>>>
>>> At the risk of giving more useful answers to the wrong question, i
>>> will say that we could do something other than require ancillary or
>>> coordinate variables to only have dimensions that the parent
>>> variable has. There just must be a simple and explicit rule for
>>> mapping between parent and child dimension.
>>>
>>> We went down that path with DSG, in order to efficiently store
>>> ragged arrays. Another possible use case is to represent contiguous
>>> bounds, where lower_bounds(i+1) == upper_bounds(i), then one only
>>> needs n+1 values instead of 2*n.
>>>
>>> Anyway, i think the rule of only allowing dimensions that are in the
>>> parent is a good one, but for compelling use cases, we could also
>>> allow "simple and explicit" alternatives.
>>>
>>> regards,
>>> John
>>>
>>> On Tue, Dec 22, 2015 at 4:07 AM, David Hassell
>>> <d.c.hassell at reading.ac.uk <mailto:d.c.hassell at reading.ac.uk>> wrote:
>>>
>>> Hello all,
>>>
>>> Many thanks for the replies. It seems there is only support for the
>>> case that ancillary variable dimensions must be a subset of their
>>> parent variable dimensions (treating scalar coordinate variables
>>> like
>>> size 1 coordinate variables for the sake of a snappier sentence
>>> - oh,
>>> that's blown it).
>>>
>>> This reminded of an old thread about this that Mark started
>>> (http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2013/056162.html).
>>> In
>>> this thread Jim convincingly argues for an ancillary variable which
>>> can have size-greater-than-one dimensions which the parent variable
>>> does not span
>>> (http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2013/056215.html):
>>>
>>> "As an example, let's say that I have a variable a[X,Y,T], which
>>> contains the total energy deposited per day into the
>>> atmosphere by
>>> charged particles (from the solar wind & Van Allen belts) on a
>>> lon/lat grid as a function of time. (Something I used to work on
>>> many years ago.) Let's then say that I have another variable,
>>> b[X,Y,Z], which represents the model atmosphere density
>>> profile on
>>> the same lon/lat grid as a function of altitude. This density
>>> profile was used in the calculation of the energy deposition
>>> values
>>> stored in variable a. Variable b is clearly valid as an
>>> ancillary
>>> variable for a, isn't it?"
>>>
>>> Mark raised a defect ticket (#98) about this, but withdrew it in
>>> light
>>> of the lack of supprt from the mailing list discussion.
>>>
>>> However, variable b in Jim's example seems to me to be storing
>>> "sub-grid scale information", so if we are to allow that we
>>> perhaps we
>>> ought to allow coordinate variables which sub-grid values and
>>> which do
>>> not span their any of their variable dimensions. For example, we
>>> might
>>> want to store the longitude coordinates which contributed to a zonal
>>> mean. The size 1 dimension case I originally raised is merely a
>>> special case of this, I feel.
>>>
>>> But I do not think that there is any appetite for this at this time,
>>> and certainly not from me. John - your comment here was actually
>>> very
>>> useful!
>>>
>>> So, I now think that ancillary variable dimensions should be a
>>> subset
>>> of their asssociated data variable dimensions (which includes the
>>> possibility of ancillary variables have no dimensions). Perhaps, in
>>> the new year, ticket #98 could be reopened as an enhancement ...
>>>
>>> All the best,
>>>
>>> David
>>>
>>>
>>> ---- Original message from Karl Taylor (01PM 21 Dec 15)
>>>
>>> > Date: Mon, 21 Dec 2015 13:59:33 -0800
>>> > From: Karl Taylor <taylor13 at llnl.gov <mailto:taylor13 at llnl.gov>>
>>> > To: cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>
>>> > Subject: Re: [CF-metadata] [CF Metadata] Question about ancillary
>>> > variables/formula terms variables
>>> > User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0)
>>> > Gecko/20100101 Thunderbird/38.4.0
>>> >
>>> > Hi David,
>>> >
>>> > I can't think of anyone needing these constructs, although
>>> there are
>>> > cases when both the "parent" and ancillary or formula_terms
>>> variable
>>> > might *both* have a scalar dimension.
>>> >
>>> > Karl
>>> >
>>> > On 12/21/15 7:41 AM, David Hassell wrote:
>>> > >Hello,
>>> > >
>>> > >I was wondering if anyone has ever had use for an ancillary
>>> variable
>>> > >(or data variable pointed to from a formula_terms attribute),
>>> having a
>>> > >size 1 dimension which the "parent" field does *not* have. The
>>> > >convention do not say anything about this.
>>> > >
>>> > >For example:
>>> > >
>>> > > dimensions:
>>> > > t = 1;
>>> > > x = 96;
>>> > > y = 73;
>>> > > variables:
>>> > > float q(x, y) ;
>>> > > q:standard_name = "specific_humidity" ;
>>> > > q:units = "g/g" ;
>>> > > q:ancillary_variables = "q_error_limit" ;
>>> > > float q_error_limit(t, x, y)
>>> > > q_error_limit:standard_name = "specific_humidity
>>> standard_error" ;
>>> > > q_error_limit:units = "g/g" ;
>>> > >Similary for a scalar coordinate variable, which is logically
>>> > >equivalent to the size 1 dimension case (this time shown on a
>>> formula
>>> > >terms variable):
>>> > > dimensions:
>>> > > x = 96;
>>> > > y = 73;
>>> > > z = 19;
>>> > > variables:
>>> > > float q(z, x, y) ;
>>> > > q:standard_name = "specific_humidity" ;
>>> > > q:units = "g/g" ;
>>> > > float z(z):
>>> > > z:standard_name = "atmosphere_hybrid_height_coordinate";
>>> > > z.formula_terms = "a: var1 b: var2 orog: var3"
>>> > >
>>> > > float var3(x, y):
>>> > > time:coordinates = "time";
>>> > >
>>> > > float time:
>>> > > time:standard_name = "time";
>>> > > time:units = "days since 2000-12-1";
>>> > >
>>> > >Thanks for your help,
>>> > >
>>> > >All the best,
>>> > >
>>> > >David
>>> > >
>>> > >
>>> > >--
>>> > >David Hassell
>>> > >National Centre for Atmospheric Science (NCAS)
>>> > >Department of Meteorology, University of Reading,
>>> > >Earley Gate, PO Box 243,
>>> > >Reading RG6 6BB, U.K.
>>> > >
>>> > >Tel : +44 118 3785613
>>> > >E-mail: d.c.hassell at reading.ac.uk
>>> <mailto:d.c.hassell at reading.ac.uk>
>>> > >_______________________________________________
>>> > >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 <mailto:CF-metadata at cgd.ucar.edu>
>>> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>
>>>
>>> --
>>> David Hassell
>>> National Centre for Atmospheric Science (NCAS)
>>> Department of Meteorology, University of Reading,
>>> Earley Gate, PO Box 243,
>>> Reading RG6 6BB, U.K.
>>>
>>> Tel : +44 118 3785613 <tel:%2B44%20118%203785613>
>>> E-mail: d.c.hassell at reading.ac.uk <mailto:d.c.hassell at reading.ac.uk>
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>>>
>>>
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>>
>>
>>
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