[CF-metadata] ungridded data

From: Brian Eaton <eaton>
Date: Thu, 20 Jun 2002 19:13:36 -0600 (MDT)

Hi Bob,

> The humidity variable represents station data which may or may not have a related
> grid. The ps variable does have a related reduced grid, but no boundary variables
> are defined, so it is 'implicit'. Structurally the two are identical.

Actually they're not identical. The "rgrid" dimension has an associated
coordinate variable which has the "compress" attribute which tells you how
to scatter the data back to a 2D array. That's how an application would
identify a reduced grid.

Your assumption that the reduced grid has implicit cells is not necessarily
true. Our atmospheric model uses the reduced grid with a spectral
representation of the primitive equations which doesn't need to know
anything about cells.

> So I'm left with the operating definition, not entirely satisfactory, that a
> variable is gridded if it has associated coordinate and/or auxiliary coordinate
> variables with boundaries.

I agree with Jonathan that boundary data is not essential. Many models
output point/instantaneous data and will not include boundary data with the
output coordinate data. If an application represents this type of data by
using filled cells then it must make assumptions about the cell locations.
But point data can also be represented by contouring which doesn't require
assumptions about cell locations.

Brian
Received on Thu Jun 20 2002 - 19:13:36 BST