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| puck2017 |
12/10/2007 09:45PM (Read 5776 times)
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Status: offline
Registered: 12/10/2007
Posts: 2
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I am looking for some help understanding the FITS standard for encoding an astrometric solution in the header. Specifically, is the cos(dec) correction for RA supposed to be encoded in the CDm_n/CDELTn keywords, or is it understood that it will be applied by the FITS reader after the fact?For example, if you had an image with 0.28"/pixel at a declination of 30 degrees, and keyword headers:
CTYPE1 = 'RA---TAN '
CDELT2 = 0.000078
would you expect to see:
CDELT1 = -0.000078
or:
CDELT1 = -0.000090
?Also, do you have a feel for whether there are groups out there that are not following the standard? If there are, then how is the FITS reader software supposed to determine whether or not to apply the correction?
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| fitz |
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12/10/2007 09:45PM
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Status: offline
Registered: 09/30/2005
Posts: 4040
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See Frank's reply in https://iraf.net/phpBB2/viewtopic.php?t=86862
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Astrometry header standard for FITS?
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