[CF-metadata] the need to store lat/lon coordinates in a CF-compliant netCDF file

From: Bentley, Philip <philip.bentley>
Date: Wed, 3 Aug 2011 14:48:13 +0100

Dear Heiko,

> I hope CF could define a default datum, e.g. the GRS1980
> Authalic Sphere, since this matches most closely with
> existing software (netcdf-java). This would make live easier
> for the software-developers who have to use something if
> nothing is given.

I'm not sure that defining a default datum for CF is the right way to go
in this instance. I would have thought that if a particular piece of
data analysis is at a resolution that requires a geodetic datum to be
specified then, in absentia the actual one being defined in metadata,
it's not clear to me that using some semi-arbitrary, and potentially
invalid, default datum is any better than giving the user the
opportunity to select the one s/he believes to be the most appropriate
for the task in hand.

The current CF conventions include a (fairly minimal) set of metadata
attributes which can be used to describe the basic properties of the
coordinate reference system associated with a given dataset. The onus
then is on data producers to utilise those metadata attributes to
describe their data to the fullest extent possible. Furthermore, other
non-CF attributes may be used to augment the standard set - over time
some of these additional attributes would no doubt find their way into
the CF specification.

Ultimately, if end-users consider that a given dataset has insufficient
metadata to justify its use within a particular context, then they can
always choose to ignore that dataset. With the passage of time - and in
true Darwinian fashion - such datasets (and their producers) will find
that they are increasingly disregarded/overlooked in analyses. Hopefully
this would galvanise such data producers into improving the quality of
their spatial metadata!

Regards,
Phil


PS: if a default datum were to be encoded into the CF conventions, I'd
imagine that the WGS84 datum would be the way to go rather than GRS80
which, if I understand correctly, has somewhat more of a bias towards
use over the North American continent. That said, I suspect the
differences between the 2 datums are sufficiently small as to get lost
in the underflow for many metocean research applications.
Received on Wed Aug 03 2011 - 07:48:13 BST