[CF-metadata] curvilinear cartesian coordinates case

From: Brian Eaton <eaton>
Date: Sat, 25 Nov 2006 09:17:12 -0700

Hi Bert,

On Fri, Nov 24, 2006 at 08:10:03PM +0100, Bert Jagers wrote:
>
> >>* I would prefer an extension of the "grid mappings and projections" with
> >>the attribute "mapped_coordinates" for models using curvilinear cartesian
> >>coordinates.
> >I think it is fine to have auxiliary coordinates of x y lat lon all at the
> >same time, as in your example. You say that
> >"What is lacking in this example is some clue that x and y are the
> >coordinates in the Lambert projection."
> >but that should be clear from their standard names of
> >projection_x_coordinate
> >and projection_y_coordinate, shouldn't it?
> It might work like that. One could search all variables in the file for
> projection_x/y_coordinate defined on a subset of the dimensions of the data
> array. Hm, why was the coordinates attribute introduced if one can do it
> like that (just scan for variables with names latitude and longitude)? The
> only problem can occur when there are two sets of x/y projection
> coordinates with the same dimensions. That can happen if there are two data
> sets in the file with the same dimensions defined at different locations,
> e.g. staggered data. However, this case is circumvented by defining
> different dimension variables instead of reusing them. Another problem
> would be the case in which you may have two projections lat/lon coordinates
> (e.g. at the border of two countries with different national coordinate
> systems). I must admit this is a rare case, but not completely impossible
> (I am involved in such a project, but it is not yet using netCDF). However,
> in such case there is a larger problem namely that the association between
> projection_x/y_coordinate and related grid_mapping is lost. My previous
> solution doesn't help to solve that case either. I would suggest that the
> attribute "grid_mapping" should not be associated with the data variables
> as presented in section 5.6 of Conventions 1.0 but with the auxiliary
> coordinates. Any pair of projection_x/y_coordinates with appropriate
> dimensions and consistent grid_mapping could be used for plotting.

Could you please provide a CDL example that shows how the association
between the projection_x/y_coordinate and related grid_mapping is lost when
the grid_mapping is attached to the data variable.

Thanks,
Brian
Received on Sat Nov 25 2006 - 09:17:12 GMT