[CF-metadata] axis attribute

[John Caron]

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?