[AstroPy] AstroPy Digest, Vol 113, Issue 5

Sun Feb 14 11:33:34 EST 2016

> So how would I go about creating a new image file with the same image dimesions (which are given by NAXIS1 x-axis and NAXIS2 y-axis)?

You may not want to use the naxis1/2 keywords directly, but instead use the image shape of the original image:

    newdata = np.empty_like( hima_sk_um2[1].data)

    <fill/assign data>

    hdu = ImageHDU(newdata)   # or PrimaryHDU(newdata)
    HDUList([hdu]).writeto('newfile.fits')

The np._like functions (ones_like, zeros_like, empty_like) take an existing array and create a similar one (same dimensions and type) with ones, zeros or empty (random) values.

The header is implicitly created in the call to ImageHDU or PrimaryHDU, and will have the right naxis etc information.

> I'm hoping this question is relatively straightforward for those proficient with IDL and python and fits file handling (I'm using the astropy.fits module)
> 
> 
> I'm looking to find an equivalent to SXPAR (whose function is to obtain the value of a parameter in a FITS header) from IDL into python...
> 
> 
> http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro
> 
> "sxpar.pro" - idlastro.gsfc.nasa.gov<http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro>
> idlastro.gsfc.nasa.gov
> Apostrophes are stripped ; from strings. If the parameter is logical, 1b is ; returned for T, and 0b is returned for F. ; If Name was of ...
> 
> 
> This is the original code in IDL:
> 
> nxpix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS1')
> 
> nypix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS2')
> 
> This is my conversion attempt into python using astropy.fits:
> 
> from astropy.io import fits
> 
> 
> hima_sk_um2 = fits.open('') #Will contain the directory extension to the fits/img file I wish to open
> 
> 
> # Compute the size of the images (you can also do this manually rather than calling these keywords from the header):
> 
> nxpix_um2_ext1 = hima_sk_um2[1].header['NAXIS1']
> 
> nypix_um2_ext1 = hima_sk_um2[1].header['NAXIS2']
> 
> Firstly, is this correct? And secondly, is this the best way to handle an extension value?
> 
> Any advise would be warmly received.
> 
> Many thanks,
> 
> Michael
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> Message: 2
> Date: Sun, 14 Feb 2016 14:37:12 +0000
> From: Kevin Gullikson <kevin.gullikson at gmail.com>
> To: Astronomical Python mailing list <astropy at scipy.org>
> Subject: Re: [AstroPy] Equivalent expression for SXPAR from IDL in
>        python
> Message-ID:
>        <CAEUX0Xf=Azcuf-v9aD046iY0ji0z+2htFjpwkktKkYBEXPzaPQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> 
> If all you want is the header, you can call
> 
> header = fits.getheader(filename, extension_number)
> 
> That is a bit simpler, and might be a bit faster too (not sure).
> 
> On Sun, Feb 14, 2016 at 6:48 AM Roberts, Michael <
> michael.roberts.15 at ucl.ac.uk> wrote:
> 
>> I'm hoping this question is relatively straightforward for those
>> proficient with IDL and python and fits file handling (I'm using
>> the astropy.fits module)
>> 
>> 
>> I'm looking to find an equivalent to SXPAR (whose function is to obtain
>> the value of a parameter in a FITS header) from IDL into python...
>> 
>> 
>> http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro
>> "sxpar.pro" - idlastro.gsfc.nasa.gov
>> <http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro>
>> idlastro.gsfc.nasa.gov
>> Apostrophes are stripped ; from strings. If the parameter is logical, 1b
>> is ; returned for T, and 0b is returned for F. ; If Name was of ...
>> 
>> This is the original code in IDL:
>> 
>> nxpix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS1')
>> 
>> nypix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS2')
>> 
>> This is my conversion attempt into python using astropy.fits:
>> 
>> from astropy.io import fits
>> 
>> 
>> hima_sk_um2 = fits.open('') #Will contain the directory extension to the
>> fits/img file I wish to open
>> 
>> 
>> # Compute the size of the images (you can also do this manually rather
>> than calling these keywords from the header):
>> 
>> nxpix_um2_ext1 = hima_sk_um2[1].header['NAXIS1']
>> 
>> nypix_um2_ext1 = hima_sk_um2[1].header['NAXIS2']
>> 
>> Firstly, is this correct? And secondly, is this the best way to handle an
>> extension value?
>> 
>> Any advise would be warmly received.
>> 
>> Many thanks,
>> 
>> Michael
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at scipy.org
>> https://mail.scipy.org/mailman/listinfo/astropy
>> 
> --
> Kevin Gullikson
> PhD Candidate
> University of Texas Astronomy
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> ------------------------------
> 
> Message: 3
> Date: Sun, 14 Feb 2016 11:08:22 -0500
> From: Paul Barrett <pebarrett at gmail.com>
> To: Astronomical Python mailing list <astropy at scipy.org>
> Subject: Re: [AstroPy] Equivalent expression for SXPAR from IDL in
>        python
> Message-ID:
>        <CAOqsD136udHzAhySoxn7OdVsuF5VMREm-LRDy+oUwX5ykT2cJg at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> 
> astropy.io.fits.open(filename)[0]['NAXIS1'] will give you the value of the
> NAXSI1 keyword in the primary header.
> 
> In the Python FITS library, a FITS file is a list of headers and each
> header is a list of rows.  The value of a keyword can be obtained by
> specifying the header name or index, and the keyword name as show above.
> 
> 
> On Sun, Feb 14, 2016 at 7:47 AM, Roberts, Michael <
> michael.roberts.15 at ucl.ac.uk> wrote:
> 
>> I'm hoping this question is relatively straightforward for those
>> proficient with IDL and python and fits file handling (I'm using
>> the astropy.fits module)
>> 
>> 
>> I'm looking to find an equivalent to SXPAR (whose function is to obtain
>> the value of a parameter in a FITS header) from IDL into python...
>> 
>> 
>> http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro
>> "sxpar.pro" - idlastro.gsfc.nasa.gov
>> <http://idlastro.gsfc.nasa.gov/ftp/pro/fits/sxpar.pro>
>> idlastro.gsfc.nasa.gov
>> Apostrophes are stripped ; from strings. If the parameter is logical, 1b
>> is ; returned for T, and 0b is returned for F. ; If Name was of ...
>> 
>> This is the original code in IDL:
>> 
>> nxpix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS1')
>> 
>> nypix_uw1_ext1 = sxpar(hima_sk_uw1_ext1,'NAXIS2')
>> 
>> This is my conversion attempt into python using astropy.fits:
>> 
>> from astropy.io import fits
>> 
>> 
>> hima_sk_um2 = fits.open('') #Will contain the directory extension to the
>> fits/img file I wish to open
>> 
>> 
>> # Compute the size of the images (you can also do this manually rather
>> than calling these keywords from the header):
>> 
>> nxpix_um2_ext1 = hima_sk_um2[1].header['NAXIS1']
>> 
>> nypix_um2_ext1 = hima_sk_um2[1].header['NAXIS2']
>> 
>> Firstly, is this correct? And secondly, is this the best way to handle an
>> extension value?
>> 
>> Any advise would be warmly received.
>> 
>> Many thanks,
>> 
>> Michael
>> 
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at scipy.org
>> https://mail.scipy.org/mailman/listinfo/astropy
>> 
>> 
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