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Using header items from different sources
So far, header items have been assumed to originate only from one
source (FITS). In reality, an image may have more than one
set of header information, and these are distinguished by giving them
different names. FITS headers are normally used for storing
information that may be widely distributed, perhaps to people using
different data reduction systems, whereas more private collections of
header information may be created by using a name of your own
choice. Private header information has the advantage that it is
unlikely to be trampled on by other software (that believes it knows
what the headers mean - rightly or wrongly) and is typically used for
information needed only within a particular software
package.3
Using header items from other sources is achieved simply by replacing
' ' (which is a synonym for 'FITS') with the appropriate
name. Storing information in a named source solely used by your
programs is encouraged. This is better than trusting other programs
not to modify values that you have set. 'MYSOURCE' is used in
the following examples:
* Write a new header item.
CALL HDR_OUT( 'OUT', 'MYSOURCE', ITEM, ' ', VALUE, ISTAT )
...
* Read back the value.
CALL HDR_IN( 'IN', 'MYSOURCE', ITEM, 1, VALUE, ISTAT )
Next: Accessing header items by index
Up: More advanced header access
Previous: Accessing header items using different data types
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