Hi John,
CF sec 5.6 has an example of how to represent the rotated pole grid.
The "axis" attribute is not well defined for any use other than it's
original one which is that it provides an easy way to identify
lat,lon,lev,time axes without having to parse the "units" attribute.
It has always been only an optional attribute in CF. It was included for
backwards compatibility with the GDT convention which was one of the
precursors to CF.
Brian
On Mon, Nov 13, 2006 at 12:37:59PM -0700, John Caron wrote:
>
>
> Brian Eaton wrote:
> >Hi Jonathan,
> >
> >Here is the note that resulted in the wording of CF sec 4.1:
> >
> >On Wed, 12 Dec 2001, Jonathan Gregory wrote:
> >
> >>Returning to the use of latitude and longitude for things which aren't
> >>really.
> >>I am happy with what we decided, but another possible pitfall has
> >>occurred to
> >>me. In the case of a rotated pole, it would be very natural for a
> >>data-writer
> >>to use standard-looking lat and lon axes for the *rotated* lat and lon.
> >>If we
> >>don't want this, we ought to specifically forbid it, I would suggest, by
> >>adding notes in 4.1 and 4.2 e.g.
> >>
> >>Coordinates of latitude with respect to a rotated pole should be given
> >>units
> >>of "degrees", not "degrees_north" or equivalents, because applications
> >>which
> >>use the units to identify axes would have no means of distinguishing such
> >>an
> >>axis from real latitude, and might draw incorrect coastlines, for
> >>instance.
> >>It would also not generally be appropriate to attach an axis attribute to
> >>a
> >>rotated-latitude coordinate variable. Such a variable can be identified by
> >>a standard_name of "grid_latitude".
> >
> >
> >I believe that the reason for excluding the use of "axis" is that the
> >default interpretation of axis="X" is to identify the longitude axis.
> >Allowing axis="X" to denote either the rotated latitude or longitude axes
> >is a recipe for confusion and unlikely to be helpful to any application.
>
> Hmm, I was thinking the main reason to identify axis=X was for projection
> coordinates, which these can be seen as analogous to. But now I realize
> that we look for the standard name "projection_x_coordinate", so maybe
> thats wrong.
>
> Still, the question remains how to represent rotated lat/lon in CF?
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Received on Mon Nov 13 2006 - 12:58:16 GMT
