[CF-metadata] axis attribute

From: John Caron <caron>
Date: Thu, 23 Nov 2006 10:32:22 -0700

Jonathan Gregory wrote:

>I've argued so far in favour of restricting axis X and Y to 1D lon and lat
>coord variables. Now I'd like to argue the alternative of generalising them
>to be used with any 1D horizontal coord variables i.e. removing the exclusion
>that they can't be used for rotated lon and lat.
>
>For 1D lon and lat, the axis attribute is still redundant while we adhere to
>COARDS, because such coord vars must be identifiable by units (and can
>optionally also be identified by standard name). However for other horizontal
>coordinates the axis attribute is not redundant if generalised. It tells you
>that this axis is a horizontal axis. If you had some non-spatiotemporal
>axes e.g. realization or land cover type, it might be useful to be told which
>of the axes are the horizontal coordinates, since this is not easy to deduce
>from the standard names without some intelligence. Is it useful to know?
>
>
Perhaps this is not an intrinsic property of the data, but more of a
plotting preference?

>I think the choice of X and Y is arbitrary. Both of them indicate horizontal,
>and the only difference is a preferred choice for plotting, I imagine. Rotated
>lon is not necessarily X, for instance, if the pole is tipped over a long way.
>
>I would not favour allowing X and Y on 2D aux coord variables. I think that
>in cases where there are 2D horizontal aux coord variables, the X and Y
>designations still properly belong to the 1D axes e.g. the projection coords.
>Because these axes are thus designated, you can tell which 2D coord vars are
>horizontal; they have dimensions belonging to axes which are labelled with
>X and Y. Perhaps we should make it mandatory to attach standard_names of
>longitude and latitude to 2D auxiliary lon and lat variables so that they can
>be easily identified as such.
>
>
I agree with mandatory standard_names for 2D lat, lon.
Received on Thu Nov 23 2006 - 10:32:22 GMT