[AstroPy] Loading wavelength from FITS spectrum

[Ian Crossfield]

The previously suggested solutions work for a linear wavelength 
solution, but things get more complicated for higher-order polynomial 
relations.  In these cases I use the following:

from pyraf import iraf
import numpy as np
iraf.wspectext('input.fits', 'output.txt', header=False)
wavelength_and_flux = np.loadtxt('output.txt')

I agree that it would be convenient to have an AstroPy helper function 
for doing this sort of thing.

-Ian



On 7/4/13 10:57 AM, Thøger Rivera-Thorsen wrote:
> I usually go:
>
> data, header = pyfits.getdata(fitsfile, header=True)
> wave = numpy.arange(data.shape[0]) * header['CDELT1'] + header['CRVAL1']
>
> That should be about as simple as it gets :-)
>
> Cheers,
> Emil
>
>
>
> On 2013-07-04 10:43, Éric Depagne wrote:
>> Le jeudi 4 juillet 2013 à 03:51:20, Gustavo Bragança a écrit :
>>> Hi,
>>>
>> Hi Gustavo,
>>
>>> Is there any easy way to load the values of wavelength from a FITS spectrum
>>> using astropy?
>>>
>>> I could obtain the wavelengths by using some values of the header, but I
>>> was wondering if there is an easy way.
>>>
>> I use the following code to get the wavelength and intensity:
>> def readspec(fitsfile):
>>           f = pyfits.open(fitsfile)
>>           cdelt1 = f[0].header['CDELT1']
>>           crval1 = f[0].header['CRVAL1']
>>           start = crval1 - f[0].header['CRPIX1'] * cdelt1
>>           end = start + cdelt1 * f[0].shape[0] - cdelt1/10.
>>           x = numpy.arange(start, end, cdelt1)
>>           f.close()
>>           return x, f[0].data
>>
>> I'm not sure it's the best way to do so, but it works.
>>
>> HTH.
>>
>> Éric.
>>
>> Un clavier azerty en vaut deux
>> ----------------------------------------------------------
>> Éric Depagne                            eric at depagne.org
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at scipy.org
>> http://mail.scipy.org/mailman/listinfo/astropy
> _______________________________________________
> AstroPy mailing list
> AstroPy at scipy.org
> http://mail.scipy.org/mailman/listinfo/astropy


-- 
Ian Crossfield
http://www.mpia-hd.mpg.de/homes/ianc/
Max-Planck-Institut für Astronomie
+49-(0)6221 528-405
Room 308/4