[AstroPy] Parameter 'origin' in WCS-methods
mdroe at stsci.edu
Fri May 8 08:48:34 EDT 2009
The distortion table lookup is non-invertible (without doing some sort
of iterative approximation) -- so that's unimplemented. There are some
good examples in Paper IV as to why it isn't really possible in a
general sense -- but it may be reasonable assuming that the lookup table
fits certain characteristics.
SIP is only invertible if a set of inverted coefficients is provided in
the header, which we support but don't require.
So it's more "difficult" than "impossible" -- it just isn't something
we've had an immediate need for here (which is primarily within the new
version of MultiDrizzle).
Martin Kuemmel wrote:
> Thanks for explaining the 'origin'. Actually I had read
> these pages, but not carefully enough, obviously
> Next question:
> There is the method 'all_pix2sky(origin, *args)' to get sky coordinates,
> which includes "everything" (SIP, distortion, wcslib). There is no
> method 'all_sky2pix(origin, *args)'.
> Is it planned to have to implement this? Or is it difficult/impossible?
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