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
