John & Co,
> Also, they are wondering what to use for the default ellipsoid when these
> are not specified. It seems to me the obvious candidates are 1) spherical
> earth with a standard radius, or 2) WGS84 ellipsoid.
I imagine the vast majority of netcdf datasets fall into this camp. I
had an interesting talk yesterday with Dave Blodgett, who pointed out
that even though most models are running on a spherical earth, they
mostly likely do not transform the initial bathymetry/topography,
coastline, and other model inputs into spherical earth coordinates,
but just leave them in their original datum, which is usually WGS84.
So it seems that your 2) would be more likely to be right.
And just to make sure that CFers are on the same page, if the datum is
actually known to be different, it can be specified using the CF datum
parameters ("inverse_flattening" and "earth_radius", or
"semi_major_axis" and "semi_minor_axis" in CF 1.5
(http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/apf.html) where
the doc now states: "The attributes which describe the ellipsoid and
prime meridian may be included, when applicable, with any grid
mapping."
-Rich
On Tue, Feb 1, 2011 at 2:40 PM, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
> Apparently ESRI is willing to add support for CF 1.5 grid_mapping attributes
> for ellipsoidal-earth/geodetic-datum definitions in the Grid Mappings and
> Projections specification.
>
> They are looking for sample data, especially using ellipsoidal parameters
> (semi_major_axis/semi_minor_axis/inverse_flattening). Does anyone have any?
>
> Also, they are wondering what to use for the default ellipsoid when these
> are not specified. It seems to me the obvious candidates are 1) spherical
> earth with a standard radius, or 2) WGS84 ellipsoid.
>
> Opinions?
>
> John
>
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--
Dr. Richard P. Signell (508) 457-2229
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598
