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.greg...@reading.ac.uk> > To: cf-metadata@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 > _______________________________________________ > CF-metadata mailing list > CF-metadata@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 E-mail: d.c.hass...@reading.ac.uk _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata