Hi Folks
I've not been following this in as much detail as I'd like, but I'd make
the observation that the change from
- physical quantity on a physical grid to
- a fourier transform (in one or more spatial dimensions) to
- spherical harmonics
hasn't changed *what* is measured, nor where, it is, as Benno states, a
transformation. We don't give things different standard names when
they're on different physical grids, or do we ...
(Then we have the situation where we have a FT in time, which again,
logically, hasn't changed what has been measured, but simply changed the
4d grid.)
... yes we do.
We do split the vector components on a physical grid, so if we did a
regrid from a lat/lon grid, to, say, a polar stereographic grid, the
data has been reprojected and information has been propagated between
things - ie the same information now has been projected into quantities
with different standard names.
So I don't think what we have done gives us a hard and fast rule about
what we *should* do here, but it perhaps suggests that Jonathan's
position is close to the status quo.
BUT
> 3) CF should handle spectral harmonics as well.
>> Yes, when it is requested to do so.
We would write spherical harmonic data now in CF if we could! But there
are only so many things we can push at any one time ...
>I'd probably agree with you that in that case we would have a
coordinate dimension, because it would be multivalued and
>the number and identity of the components would depend on the spectral
>resolution.
seems like an argument for solving Fourier Transforms in the same way. I
think overloading cell-methods would be a dead end for this direction.
However, despite the discussion thus far, I'm not entirely sure I
understand exactly what Benno is proposing, not least because there are
different ways of arranging FT components in an array - or exactly what
Jonathan is implying for spherical harmonics.
Bryan
On Thursday 17 Jun 2010 16:41:37 Jonathan Gregory wrote:
> Dear Brian
>
> > Isn't the use of "cell_methods" with a value of "variance" an
> > example where we don't require a different standard_name even
> > though the units are different?
>
> Yes. I simplified what I said in order not to be confusing, but
> perhaps the result was confusing! Cell methods specifies statistical
> computations done on the values of the variable in order to
> represent its subgrid variation, and the resulting statistic might
> have a different unit.
>
> Maybe cell_methods could be extended to represent some kinds of
> transformation, such a calculating a probability density function or
> a Fourier transform. That would be new kind of purpose for it. I
> don't see a reason to prefer that to using the standard name to
> indicate the transformation, though, following the the guidelines
> for construction of standard names.
>
> Best wishes
>
> Jonathan
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
--
Bryan Lawrence
Director of Environmental Archival and Associated Research
(NCAS/British Atmospheric Data Centre and NCEO/NERC NEODC)
STFC, Rutherford Appleton Laboratory
Phone +44 1235 445012; Fax ... 5848;
Web: home.badc.rl.ac.uk/lawrence
Received on Thu Jun 24 2010 - 04:45:55 BST
