Requests to assign values to the following reserved keywords in the FITS extension are ignored: SIMPLE, BITPIX, NAXIS, NAXISn, EXTEND, PCOUNT, GCOUNT, XTENSION, BLOCKED, and END.
Only scalar or one-element vector components may be transferred to the FITS extension.
The data type of the component selects the type of the FITS value.
If the destination keyword exists, the existing value and comment are replaced with the new values.
If an error is found within a line, processing continues to the next line and the error reported.
To be sure that the resultant FITS extension is what you desired, you should inspect it using the command FITSLIST before exporting the data. If there is something wrong, you may find it convenient to use command fitsedit to make minor corrections.
Field 1: The name of the input extension component whose value is to be copied to the
FITS extension. For example,
CCDPACK.FILTER would copy the value of the component
called FILTER in the extension called CCDPACK; and
IRAS90.ASTROMETRY.EQUINOX would copy
the value of component EQUINOX in the structure ASTROMETRY in the extension IRAS90. The
extension may not be FITS.
Field 2: The name of the FITS keyword to which the value is to be copied. Hierarchical
keywords are not permissible. The keyword name may be followed by a further keyword
name in parentheses (and no spaces). This second keyword defines the card before which
the new keyword is to be placed. If this second keyword is not present in the FITS
extension or is not supplied, the new header card is placed at the end of the existing
cards, but immediately before any END card. For example,
write the keyword EQUINOX immediately before the existing card with keyword
EPOCH. FITS keywords are limited to 8 characters and may only comprise uppercase
alphabetic characters, digits, underscore, and hyphen. While it is possible to have
multiple occurrences of the same keyword in a FITS header, it is regarded as bad
practice. For this and efficiency reasons, this programme only looks for the
first appearance of a keyword when substituting the values, and so only the
last value inserted appears in the final FITS extension. (See
Field 3: The comment to appear in the FITS header card for the chosen keyword. This field is optional. As much of the comment will appear in the header card as the value permits up to a maximum of 47 characters.
Comments may appear at any point in the table and should begin with an exclamation mark. The remainder of the line will then be ignored.
"A User’s Guide for the Flexible Image Transport System (FITS)", NASA/Science Office of Science and Technology (1994).
The replacements are made in blocks of 32 to reduce the number of time-consuming shuffles of the FITS extension. Thus it is possible to locate a new keyword before another keyword, provided the latter keyword appears in an earlier block, though reliance on this feature is discouraged; instead run the application twice.
For each block the application inserts new cards or relocates old ones, marking each
with different tokens, and then sorts the FITS extension into the requested order,
removing the relocated cards. It then inserts the new values. If there are multiple
occurrences of a keyword, this process can leave behind cards having the token value