[AstroPy] Bug in wcs_world2pix?

[Howard Bushouse]

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
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> 
> 
> -- 
> Michael Droettboom
> Science Software Branch
> Space Telescope Science Institute
> 
> http://www.droettboom.com
> 
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