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 > > > > ------------------------------------------------------------------------ > > > > _______________________________________________ > > CF-metadata mailing list > > [email protected] > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
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