[CF-metadata] Cell methods when there are no coordinates

From: Jonathan Gregory <j.m.gregory>
Date: Sat, 9 Nov 2013 21:07:38 +0000

Dear Mark

Thanks for the clarifications in your last email. If I have understood this
correctly now, there are two needs, which might be distinct.

(1) Indicate that a collapsed (size-one) axis is an ensemble axis, although
it doesn't have a coord var or any aux coord vars. I can see that it might
well not have these vars because there might not be anything useful you could
put in them. In the absence of these vars, the dimension name in the cell
methods isn't informative. We could perhaps solve this by introducing a new
standard name such as ensemble_member_id (a string) or ensemble_member_number
(a number) or perhaps both. These could anyway be useful. These standard names
could appear in your cell_methods, following section 7.3.4, instead of the name
of the size-one dimension, indicating that the statistic applied to all the
available members of an ensemble, without needing any coord information. I
don't think this change would require an alteration to the convention.

(2) Point to the coordinate information which applied to the axis before the
collapse. This could be useful for any sort of collapsed axis, and in fact I
think we have discussed it before at some point in the last 15 years! I agree
with your suggestion that it would be logical to record this in cell_methods
as a standardised comment. An alternative would be to add an attribute to the
collapsed coord var, but you don't have those (as you say), and also the
collapse may apply to a combination of axes. You suggest listing all the coord
or aux coord vars in the cell_methods comment. Would it not be sufficient, and
more economical, to give the name of the uncollapsed dimension(s)?

Best wishes

Jonathan
Received on Sat Nov 09 2013 - 14:07:38 GMT