[AstroPy] Determining when world and pixel axes are independent

[Phil Hodge]

On 01/13/2014 02:26 PM, Perry Greenfield wrote:
> But just because one set of pixels doesn't show this, doesn't mean that another won't either (e.g., if I change only the nth coordinate, does that only change one output coordinate), so I don't think this is sufficient to show independence (but I'm not sure I understand your example).

I didn't express it well.  I meant that you could take a one-pixel step 
along each axis in pixel space, and see if only the corresponding world 
coordinate changed.  For an N-dimensional pixel space, that would be N + 
1 transformations to world coordinates (some point in the image, plus 
one pixel adjacent to that point along each axis).  But as you said, 
this would have to be checked at multiple points in the image to have 
confidence that the axes were independent.

Phil