[CF-metadata] axis attribute

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 28 Dec 2006 23:04:21 +0000

Dear John

Adding to the below of yesterday: a possible case is that the 1D horizontal
coordinate variables are just indexes, and have no standard name. This is
quite likely if the grid isn't a simple continuous transformation from some
projection plane. An example is the tripolar grid used by the ORCA/OPA/NEMO
ocean model. In that case attaching the axis attribute to such coordinate
variables is a handy way to indicate which are the horizontal dimensions. I
realise this goes against my usual preference for clever programs and stupid
files, but working it out otherwise is more awkward.

Best wishes

Jonathan


> >Requirement: A way to identify the horizontal coordinate variables.
> >
> Sorry I dont understand the requirement. Is this for the case where its
> not a lat/lon nor a projection x, y coordinate ? Is the use case
> rotated_latitude_longitude ?

The beginning of the proposal tries to answer that:

Proposal: It can be done using COARDS rules for units in the case of latitude
and longitude. In other cases (such as projection coordinates, rotated latitude
and longitude) the standard name can be used, but that requires recognising
specific names, and standard names are optional anyway.

So, the axis attribute, if present (it is optional), can be used to
identify horizontal coordinates in any case. Lat/lon, projection coordinates,
rotated lat/lon, and any other mapping which might be invented require the
software to recognise specific units or standard names for this purpose. The
axis attribute is a more general solution that works without any knowledge of
the details of the horizontal grid.
Received on Thu Dec 28 2006 - 16:04:21 GMT