Gnomonic projection:
pixel grid with
pixel,
linear,
native, &
celestial coordinates

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What aspects of the WCS proposal are specific to FITS, and what would
we do differently if starting again from scratch (e.g. XML)?

All angles in degrees?
OK, suits astronomy and software.

Lefthanded (X, Y) coordinates?
Required for but can be very
confusing.

Define the Euler angles by specifying the celestial coordinates at
the reference point (CRVALi)?
Also necessary for firstorder behaviour but complicates
nonzenithal projections.

Require at all?
Yes, it ties the celestial coordinate system to a particular point
in the image.

Encode the algorithm type in
CTYPEi?
No, too restrictive.
