Dear Jonathan,
I like the idea of name for a grid mapping that doesn't actually map,
but suggest a name of "null_mapping" (instead of "null") to better
indicate to humans that whilst the variable is not mapping, it is
doing something.
All the best,
David
---- Original message from Jonathan Gregory (02PM 11 Mar 14)
> Date: Tue, 11 Mar 2014 14:29:25 +0000
> From: Jonathan Gregory <j.m.gregory at reading.ac.uk>
> To: cf-metadata at cgd.ucar.edu
> User-Agent: Mutt/1.5.21 (2010-09-15)
> Subject: Re: [CF-metadata] Vertical datums (again)
>
> Dear David
>
> > I'm a bit confused as to the use of these grid_mapping parameters with
> > vertical coordinates - do we need new grid_mapping_names? I'm
> > thinking, for example, of linking a geoid specification to a vertical
> > "altitude" coordinate.
>
> That's a good point, thanks. I was thinking of the grid_mapping as a place to
> record the reference surface in the same way as it does for latitude_longitude,
> which was added as a "null" horizontal mapping. No "mapping" is required for
> the vertical coordinate; it just needs its reference surface (vertical datum)
> to be more precisely specified than its geophysical description of "geoid" or
> "reference_ellipsoid" alone, for some applications.
>
> I'd like to suggest we add a new grid_mapping_name of "null" to Appendix F,
> thus: "This grid_mapping does not imply any mapping of horizontal or vertical
> coordinates. Its purpose is to describe the reference ellipsoid or the geoid."
> No map parameters, no map coordinates.
>
> I would further suggest that we make latitude_longitude an alias for null.
>
> It might happen that a different reference ellipsoid is required for vertical
> and horizontal coordinates. Thanks to Mark's accepted ticket 70, this will be
> no problem; it allows there to be more than one grid_mapping, and the
> grid_mapping attribute indicates which coordinate variable each is relevant to.
>
> Best wishes
>
> Jonathan
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--
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
Received on Fri Mar 14 2014 - 06:25:09 GMT
