Hi Ed,
Recognizing that a variable contains longitude or latitude values is a
separate problem from knowing which variables contain the coordinate values
for a given variable in the file. The association between a variable that
contains field data, and the variables that describe the grid of the field
data, is *always* made using either "coordinate variables" or "auxilliary
coordinate variables". Thus no matter how many grids are present in a
single file, variables always point directly to the associated variables
that contain their grid coordinate values.
For each variable that contains field data (as opposed to coordinate data),
once you know which variables contain the coordinate values, you need to
identify what type of coordinate it is. For latitude and longitude
coordinates the units must match one of the udunits specified versions of
degrees_east or degrees_north. But these terms don't make sense for the
coordinates in the rotated pole grid. So we decided to allow the use of
the generic unit "degrees" and to use the standard_name attribute to
identify that the variable contains latitudes or longitudes relative to a
rotated pole.
Hope that helps,
Brian
On Thu, Oct 05, 2006 at 12:00:32PM -0600, Ed Hartnett wrote:
> Howdy all!
>
> Here's a question about section 5.6, Grid mappings and projections, of
> the CF document.
>
> >From the CF document:
>
> "A CF compliant application can determine that rlon and rlat are
> longitude and latitude values in the rotated grid by recognizing the
> standard names grid_longitude and grid_latitude."
>
> But if there were two rotated pole grids in the same file, then the
> standard names would not allow me to associate the appropriate rlat
> and rlon coordinates with the grid, because there would be two of
> each.
>
> Or am I missing something?
>
> Thanks!
>
> Ed
> --
> Ed Hartnett -- ed at unidata.ucar.edu
>
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://www.cgd.ucar.edu/mailman/listinfo/cf-metadata
Received on Thu Oct 05 2006 - 12:46:44 BST
