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Find physical pixel coordinates in fits file using python

I am attached to get the coordinates of the physical sky of a given pixel inside a python script. I would like to use astropy WCS, but I will do something from python.

I tried these two code snippets.

from astropy.io import fits from astropy.wcs import WCS def astropymethod1(img): # from http://astropy.readthedocs.org/en/latest/wcs/ w = WCS(img) lon, lat = w.all_pix2world( 100., 100., 1) print lon, lat def astropymethod2(img): # from http://astropy.readthedocs.org/en/latest/wcs/ hdu = fits.open(img) w = WCS(hdu[0].header) lon, lat = w.wcs_pix2world(100., 100., 1) print lon, lat

The problem is that I get an error the first time I use WCS, and the result is only the pixel values ​​that I inserted.

 WARNING: FITSFixedWarning: The WCS transformation has more axes (2) than the image it is associated with (0) [astropy.wcs.wcs]
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1 answer

The problem is that you have a file with several FITS extensions. Here is an example session showing how you can access the appropriate WCS:

 In [1]: from astropy.io import fits In [2]: h = fits.getheader('SN1415_F625W_1_drz.fits') In [3]: f = fits.open('SN1415_F625W_1_drz.fits') In [4]: f Out[4]: [<astropy.io.fits.hdu.image.PrimaryHDU at 0x106735490>, <astropy.io.fits.hdu.image.ImageHDU at 0x106749750>, <astropy.io.fits.hdu.image.ImageHDU at 0x106751310>, <astropy.io.fits.hdu.image.ImageHDU at 0x106751d10>, <astropy.io.fits.hdu.table.BinTableHDU at 0x1067dfdd0>] In [5]: from astropy import wcs In [6]: w = wcs.WCS(f[0].header) WARNING: FITSFixedWarning: The WCS transformation has more axes (2) than the image it is associated with (0) [astropy.wcs.wcs] In [7]: w.wcs.naxis Out[7]: 2 In [8]: f[0].data In [9]: w = wcs.WCS(f[1].header) In [10]: w.wcs.naxis Out[10]: 2 In [11]: f[1].data Out[11]: array([[ 0.01986978, -0.04018363, 0.03330525, ..., 0. , 0. , 0. ], [ 0.0695872 , -0.00979143, 0.00147662, ..., 0. , 0. , 0. ], [-0.09292094, 0.02481506, -0.01057338, ..., 0. , 0. , 0. ], ..., [ 0. , 0. , 0. , ..., 0.02375774, 0.0389731 , 0.03825707], [ 0. , 0. , 0. , ..., -0.01570918, -0.01053802, 0.00461219], [ 0. , 0. , 0. , ..., -0.0638448 , -0.0240754 , 0.02679451]], dtype=float32) In [12]: w.wcs_pix2world(100., 100., 1) Out[12]: [array(6.113076380801787), array(0.616758775753701)]

So, you probably want to override your method:

 def astropymethod2(img, hduid=1): # from http://astropy.readthedocs.org/en/latest/wcs/ hdu = fits.open(img) w = WCS(hdu[hduid].header) lon, lat = w.wcs_pix2world(100., 100., 1) print lon, lat
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Source: https://habr.com/ru/post/972792/

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