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A complication that we have glossed over so far is the fact that
certain FITS header items can occur more than once within an image.
Strictly, this is limited to the keywords COMMENT,
HISTORY and ' ' (blank) which are often used to
construct multi-line descriptions of the contents or history of a FITS
file. To handle this, various of the HDR subroutines are ``FITS
occurrence aware''. For instance, the fourth argument of the
HDR_IN subroutine specifies the
occurrence of the item to be read, and
HDR_OUT will append (rather than
overwriting) items with these special names.
FITS items can also have a comment associated with them (to be read by
the recipient when a FITS file is sent to another astronomical
institution). The comment string is given by the fourth argument of
the HDR_OUT subroutine, but this facility isn't available
for non-FITS header sources where this argument will simply be
ignored.
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IMG Simple Image Data Access
Starlink User Note 160
P.W. Draper
R.F. Warren-Smith
3 March 2003
E-mail:P.W.Draper@durham.ac.uk
Copyright © 2000-2003 Council for the Central Laboratory of the Research Councils