[AstroPy] Determining when world and pixel axes are independent

[Chris Beaumont]

Hi,

Given a WCS object, I'd like to know which pixel and world axes are
independent of each other. For example:

 * X/Y are generally NOT orthogonal to RA or DEC in the tan projection (to
compute RA or DEC, you need both X and Y)
 * X is independent to DEC in cartesian projection, UNLESS something like
cd2_1 or crota are nonzero
* the velocity axis in a spectral data cube is usually orthogonal to the
spatial axes (you can translate between Z and V without knowledge of X and
Y).

I'm sure there are lots of corner cases here. Is there any way I can
introspect a WCS object to generally determine if a given world and pixel
axis are independent of each other?

Thanks,
Chris
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/astropy/attachments/20140113/b95f075e/attachment.html>