[AstroPy] Bug in wcs_world2pix?

[Michael Droettboom]

Sorry for the confusion -- I wrote this based on what the wcslib code 
does, forgetting that it primarily works in lon, lat internally, before 
converting to ra, dec at a later stage.

Mike

On 09/19/2014 07:47 AM, Howard Bushouse wrote:
> Huh. But that’s not how astronomers measure RA and Dec, even when translated to degrees. If I’ve got an object with an RA of 17:45:00.0 (hh:mm:ss.w) the RA in degrees is 266.25. We *never* use a negative RA. Instead of a range of -180 to 180, we use 0 to 360. Dec is the only one that ever goes negative (-90 to +90, as you indicated).
>
> -hb
>
> On Sep 18, 2014, at 8:26 PM, Michael Droettboom <mdroe at stsci.edu> wrote:
>
>> The range of ra and dec is (-180, 180) and (-90, 90) respectively.
>> (211, -26) is equivalent to (31, 26).
>>
>> Mike
>>
>> On 09/18/2014 05:04 PM, Maik Riechert wrote:
>>> Hi,
>>>
>>> I'm having some great trouble currently and am a bit confused too:
>>>
>>> wcs = WCS(header)
>>> x,y = wcs.wcs_world2pix(211, -26, 0)
>>> print x,y # 836.316942718 658.26364248
>>> ra,dec = wcs.wcs_pix2world(x, y, 0)
>>> print ra, dec # 31.0 26.0
>>>
>>> It seems like world2pix gives me bogus results. I was expecting values
>>> way outside my image area (image size is 4256x2832). Am I doing
>>> something obvious wrong?
>>>
>>> The WCS headers can be seen at http://pastebin.com/JrdiL949
>>>
>>> Thanks for the help,
>>> Maik
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy at scipy.org
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>>
>> -- 
>> Michael Droettboom
>> Science Software Branch
>> Space Telescope Science Institute
>>
>> http://www.droettboom.com
>>
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-- 
Michael Droettboom
Science Software Branch
Space Telescope Science Institute

http://www.droettboom.com