[CF-metadata] axis attribute

[Karl Taylor]

Dear all,

I'll reiterate what I said earlier (but I think somehow the email didn't 
get distributed).  I'm in favor of eliminating the apparently 
contradictory statements.  Of the two choices, perhaps least confusion 
would result from adopting Jonathan's suggestion: restrict X and Y to 
genuine longitude and latitude coordinates.

Karl

Jonathan Gregory wrote:
> Dear Simon
> 
>> Reading this has made me realize I may have a similar confusion with 
>> regards to other map projections eg Lambert conformal.  For these should 
>> the 'axis=X' attribute be attached to the grid x coordinate variable 
>> (x(x), ie the one we give the standard name 'projection_x_coordinate') 
>> or the longitude auxiliary coordinate variable (lon(y,x))?  Or should it 
>> not be used at all in this situation?
> 
> My reading of what the standard currently says is that you can use the axis
> attribute if you want to, in order to suggest which axis is the plot x-axis,
> but you don't have to, and it doesn't carry any specific meaning.
> 
> It does seem peculiar to me to allow it for the Lambert conformal but not for
> the rotated pole, doesn't it! Also, it is really not much information. An
> application could just assume the right-hand axis (in CDL notation) is the
> one intended to be the x-axis.
> 
> I can't remember what advantage we saw in allowing X and Y to be used for
> generic horizontal coordinates. At present I'd propose that we allow X and Y
> only for genuine longitude and latitude. Any comments, anyone?
> 
> Cheers
> 
> Jonathan
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