[AstroPy] Bug in wcs_world2pix?
d.berry at jach.hawaii.edu
Fri Sep 19 10:09:44 EDT 2014
On 19 September 2014 15:01, Michael Droettboom <mdroe at stsci.edu> wrote:
> On 09/19/2014 09:13 AM, David Berry wrote:
>> On 19 September 2014 13:23, Michael Droettboom <mdroe at stsci.edu> wrote:
>>> I've brought this to Mark Calabretta's attention -- he may have an idea.
>> wcslib provides an option to switch this sort of range checking on or
>> off. With pyast, I take the attitude that the answer to the question
>> (in this case) "what pixel has coords RA=211 Dec=-26" is "no pixel
>> has those coords", and so pyast will always return "NaN" values in
>> such circumstances. To return apparently usable values which are in
>> fact wrong is just asking for problems in my opinion.
> Yes, but the WCS range checking only happens for a TAN projection in the
> pixel-to-sphere direction. Not sure why that is. In this particular
> case, it's "garbage in", but "reasonable values out" from s2p, and then
> p2s can't know to complain about it. That might be something to improve
The docs for the wcsbchk function within wcslib says that if the
"bounds" value is odd, then strict bounds checking is performed for
the spherical-to-Cartesian (s2x) transformation for a TAN projection.
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