WCS questions

[Mark Calabretta]

On Thu 1996/12/12 00:15:16 GMT, William Thompson wrote
in a message to: fitsbits at fits.cv.nrao.edu

>Right, which is why it is incorrect to force solar data to be expressed in a
>spherical coordinate system.

We appear to going around in circles here.  We have a 2-D spherical surface 
embedded in a 3-D space seen in projection on the celestial sphere.  We want
to coordinatise points on the surface in one way and points in the surrounding
space in another way.  All I am saying is that, contrary to your original
statement, and I believe answering Steven Walton's original query, WCS
provides the tools to do this.  If you have to have Cartesian coordinates
with units of metres rather than solar radii, then use secondary axis
descriptors.

I'm not saying that you won't need to define a simple convention tied to the
CTYPEn (e.g. PLON/PLAT) which describes this system to the extent that points
outside the limb are valid and what their interpretation is to be.

Mark Calabretta
ATNF