On Tue, Apr 5, 2016 at 12:02 PM, Karl Taylor <taylor13 at llnl.gov> wrote:
> For unstructured grids when some cells are quadralaterals and others are
> pentagons, the convention stipulates that bounds should be dimensioned
> (n,5) so that the lat and lon locations of all 5 penatagon vertices can be
> recorded. My question is what to do about the extra vertex for the
> quadralaterals? Should we define a "missing_value" and store it in the
> unused vertex location?
>
Take a look at the UGRID conventions:
http://ugrid-conventions.github.io/ugrid-conventions/
In there, the lat-lon are specified in a nodes array, and the cells are
specified as indexes into that nodes array.
In the case of cells of different order, the "extra" indexes use a missing
value, usually -1.
That should be defined as the _FillValue.
This is under debate right now, but I think that's where it is headed:
https://github.com/ugrid-conventions/ugrid-conventions/issues/26
(someone still needs to update the text)
BTW, as I read the latest convensions:
http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html#missing-data
you want to use _FillValue if there is only one "Missing" value needed.
If so, perhaps we should make this clear in the convention document.
>
Where does the CF conventions address this issue (i.e. unstructured grids)
at all?
-CHB
--
Christopher Barker, Ph.D.
Oceanographer
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Received on Wed Apr 06 2016 - 12:44:52 BST
