i think a crucial property of coordinates is that their dimensions are a
subset of the variable's dimensions. otherwise one cant assign the correct
coordinate.
the length of a char valued coordinate is an exception, really char(n) is
logically the same as string.
while a dim=1 coordinate could be used, it would violate that simple
principle for no obvious gain. scalar here is preffered i think.
we added some language to CF recently to clarify this. not sure where it is.
john
On Mon, Dec 21, 2015 at 8:49 AM, Jim Biard <jbiard at cicsnc.org> wrote:
> David,
>
> I've not come across this particular case, but I've had cases where the
> ancillary data that I wish to store has less dimensions than the
> corresponding parent field. The Conventions seem to require that the
> dimensions all match. I'm of the opinion that it should not be so
> restrictive.
>
> In your particular instance, what is the significance of your time
> variable?
>
> Grace and peace,
>
> Jim
>
>
> On 12/21/15 10:41 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
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