[CF-metadata] polar stereographic projections

From: Jonathan Gregory <j.m.gregory>
Date: Tue, 15 Jun 2004 09:16:20 +0100

Dear Magi et al

As far as I can tell, polar stereographic and general stereographic are the
same operation, but perhaps the longitude doesn't play quite the same role.
With a general stereographic projection, the longitude and latitude of the
projection origin must be specified, and the meridian passing through the
projection origin (along its longitude) is the central meridian of the
projection, and appears as a vertical line in the middle of the map. For a
polar stereographic projection, *all* meridians pass through the projection
origin. The way to orientate the map is therefore arbitrary, so we specify
one of the longitudes (the straight vertical longitude) to be the vertical
line running upwards from the middle of the map.

But in both cases the latitude_of_projection_origin is needed, so I think
this ought to be added to the definition of polar_stereographic. It is
allowed to be -90 or +90. This could be avoided by having separate projections
of north_polar_stereographic and south_polar_stereographic but no-one does
that apparently.

I am not very well informed about map projections so if anyone else can
correct or comment on the above that will be welcome.

Cheers

Jonathan
Received on Tue Jun 15 2004 - 02:16:20 BST