John,
IMHO, I don't believe the orthographic projection would ever be used at
a sufficiently large map scale that an ellipsoidal figure of earth would
be demanded. So, yes, a spherical earth approximation should suffice.
Regards,
Phil
On Tue, 2008-05-27 at 11:38 -0600, John Caron wrote:
> Do you need ellipsoidal earth for orthographic, or is spherical sufficient?
>
> Philip Bentley wrote:
> > Hi Don,
> >
> > Vertical Perspective projection made it into CF 1.2, which is why I
> > didn't mention it. Yes, I was also assuming that GoogleEarth uses a
> > tilted perspective-type projection. But for general whole-globe views,
> > the orthographic projection is a useful alternative (and obviously the
> > limiting case of vertical perspective - i.e. the perspective point is at
> > inifinity).
> >
> > Regards,
> > Phil
> >
> > On Wed, 2008-05-21 at 07:05 -0400, Don Murray wrote:
> >> Phil/Ethan-
> >>
> >> Philip Bentley wrote:
> >>
> >> > An obvious one perhaps, but one which we may find increasingly useful /
> >> > relevant in light of the rise and rise of GoogleEarth-type applications,
> >> > is the Orthographic projection. This being the classic 'view from space'
> >> > projection.
> >> >
> >> > Same grid mapping parameters as the other azimuthal projections, viz.
> >> >
> >> > grid_mapping_name = "orthographic"
> >> >
> >> > longitude_of_projection_origin
> >> > latitude_of_projection_origin
> >> > false_easting
> >> > false_northing
> >> >
> >> > (though off the top of my head I can't think of a scenario where one
> >> > would want to use the last two params).
> >>
> >> I think GE actually uses a tilted perspective view. But,
> >> I think CF should support the Vertical Perspective with
> >> an ellipsoid. EUMETSAT has GRIB messages with this projection
> >> and an elliptical earth.
> >>
> >> Don
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
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> > CF-metadata at cgd.ucar.edu
> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
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Received on Mon Jun 02 2008 - 02:21:08 BST
