wcs.to_header() function giving mixed up header keywords

Description

There are three ways to specify the rotation/scale information. The two can be combined into one matrix (CD1_1 through CD2_2) or the rotation matrix can be given as PC1_1 through PC2_2 and the pixel scale as CDELT1/CDELT2. The third way is to give CDELT1/CDELT2 and a rotation angle as CROTA2.

What wcs.to_header() outputs looks like the second but the values of the PC matrix are actually what should be in a CD matrix and the CDELT value are nonsensical (1x1 degree pixels).

Here are the adjustments that need to be made to the headers to make them work properly:

fname, extension = os.path.splitext(file)
fits.delval(file, 'CDELT1')
fits.delval(file, 'CDELT2')
pc1_1 = fits.getval(file, 'PC1_1')
pc1_2 = fits.getval(file, 'PC1_2')
pc2_1 = fits.getval(file, 'PC2_1')
pc2_2 = fits.getval(file, 'PC2_2')
fits.setval(file, 'CD2_2', value=pc2_2, after='CRPIX2')
fits.setval(file, 'CD2_1', value=pc2_1, after='CRPIX2')
fits.setval(file, 'CD1_2', value=pc1_2, after='CRPIX2')
fits.setval(file, 'CD1_1', value=pc1_1, after='CRPIX2')
fits.delval(file, 'PC1_1')
fits.delval(file, 'PC1_2')
fits.delval(file, 'PC2_1')

Expected behavior

Actual behavior

Steps to Reproduce

1. [First Step]
2. [Second Step]
3. [and so on…]

# Put your Python code snippet here.

System Details

[saimn]

The discussion in question is probably #1084.

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