Dear Jim Yes, I suppose you're right, on reflection. I was thinking of a situation in which you were interested in the ellipsoid only for the sake of a vertical datum, rather than as a horizontal datum (which is its usual purpose in grid_mapping). However, I now understand from the discussion and explanations from Jon Blower why you cannot actually refer heights to a vertical datum without implying a particular latitude-longitude coordinate system. So the existing grid_mapping_name of latitude_longitude will be appropriate if you want to identify the geoid or ellipsoid as a vertical datum, I agree.
My understanding is now that the height is taken perpendicular to the surface, and the lat-lon is defined on the surface, so the lat-lon of the point whose height is being measured depends on the choice of surface. Please correct me if that's not right. Cheers Jonathan > I thought this was already defined. In the second paragraph of section 5.6, > it says that if you aren?t specifying a projected coordinate system (or, I > assume, a Cartesian coordinate system such as ECF), then use the name > ?latitude_longitude?. I haven?t noticed anything we?ve talked about that > would invalidate this usage. We are talking about adding vertical datum > specifications and such as further attributes to the variable, but even > latitude and longitude values can shift depending on the ellipsoid and/or > geoid being used, so these should specified even when there is no projected > coordinate system. _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
