[CF-metadata] cell metrics

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 5 Oct 2006 08:15:55 +0100

Dear Simon, Christiane, et al.

> >>>* grid_cell_area and _height. These are metrics for the grid, rather than
> >>>quantities which need standard names. Grid cell area should be specified
> >>>by a
> >>>cell_measures variable of area (CF 7.2). Grid cell height can be deduced
> >>>as the
> >>>difference between the lower and upper boundary in the vertical
> >>>coordinate. If
> >>>it has to be stored separately we could add a cell_measures for it.
> >>>
> >>Yes, I know that the cell_measures exist, but it is convenient to have
> >>the grid information stored in variables. It would be nice if these
> >>names could be added.
> >
> >Perhaps we could add standard names of area (m2) and thickness (m)?
>
> Are you suggesting this as an alternative to the use of cell_measures or
> are you just proposing standard names for the measure variables?

It is not an alternative to cell measures. The proposal, from Christiane, was
for a standard name for such quantities as data variables in their own right.
Such data variables could also be pointed to by cell_measures.

> I'm curious as to the reason for
> introducing an alternative method for specifying cell metrics in
> addition to the existing cell bounds and cell_measures? Doesn't this
> just complicate things, leading to possible confusion / ambiguity? Does
> this make the use of cell_measures optional? (...obsolete?)

I also asked whether it was necessary (in the >>>> text at the top). I think
cell_measures would in any case remain useful as a pointer to locate the
metrics easily. Sometimes cell_measures is not necessary because you could
find the metric variable by searching the file for a data variable with the
appropriate standard name (if we defined these) and the same grid as the data
variable, but this is more laborious, and as your example shows it could be
insufficient if the lat-lon coordinates are not defined. We probably had this
discussion when we introduced cell_measures. It would be interested to know if
anyone else has views.

> a) a standard name for 'cell_volume'? (since volume is already a
> standard cell_measure name), and
Yes, we could do.

> b) a new cell_measure name of 'thickness' (or height), which would refer
> to a measure variable with standard_name = 'cell_thickness'?
Yes, possibly.

Neither of these has been requested and, as usual, we would not add them unless
they were specifically asked for.

Best wishes

Jonathan
Received on Thu Oct 05 2006 - 01:15:55 BST