[CF-metadata] Polar Stereographic Projection in CF

From: Brian Eaton <eaton>
Date: Thu, 10 Oct 2002 11:00:43 -0600 (MDT)

Hi John,

CF compliance requires that the horizontal location of each grid point be
specified by latitude and longitude coordinates. In the case of a grid
resulting from a polar stereographic projection this could be accomplished
by the use of 2D lat/lon arrays as described in sec 5.2. Note that the
specification of a projection and the projection coordinates is not
sufficient for compliance.

The current working draft (linked to the CF home page as CF-1.0-beta4)
contains a new section on grid mappings and projections. The only mapping
currently provided is a rotated pole grid. We intend to handle projections
using the same mechanism, but haven't yet determined a source of key/value
pairs to describe projections. It would be best to have an external
reference for this rather than making up our own and listing them in an
appendix as we've done for the rotated pole example (which is not a
projection). Do you think the FGDC specification of projections would be
suitable for this (and could you point me towards a reference for them)?
Also, are you aware of any ISO standards related to this?

Thanks,
Brian

On Wed, 9 Oct 2002, John Caron wrote:

> IMHO, its important to store the actual projection. So the base coordinate
> system is x,y in units (typically) of "km on the projection plane". hopefully
> you are using a standard projection (eg polar stereographic), and then you use
> some well-known way of specifying the projection, eg FGDC. knowing the
> projection is necessary to allow full interoperability with GIS. This doesnt
> cost much, just 2 1D coordinate variables.
>
> In addition, you might want to encode the lat/lon positions of each grid point,
> using the 2D coordinate axes as per section 5.2. This costs 2 2D variables in
> storage, which may or may not be small compared to the size of the file.
>
> I dont see anywhere in the CF that standardizes how to specify the
> projection(?). I think its very important, perhaps it could be done for the next
> version ?
>
>
>
> Mark A Ohrenschall wrote:
>
> > Hello,
> >
> > I'm wondering if I should follow section 5.2 of the CF Conventions in
> > representing data that is in a polar stereographic projection. And at
> > the risk of belaboring the obvious, are the two-dimensional coordinate
> > variables respectively grids of latitude and longitude values for each
> > grid cell in the poloar stereographic grid?
> >
> > Thanks,
> >
> > Mark
> >
Received on Thu Oct 10 2002 - 11:00:43 BST