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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 )



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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