A FITS header is a sequence of 80-character strings, formatted according to particular rules defined by the Flexible Image Transport System (FITS). FITS is a widely-used standard for data interchange in astronomy and has also been adopted as a data processing format in some astronomical data reduction systems. The individual 80-character strings in a FITS header are usually called cards or header cards (for entirely anachronistic reasons). A sequence of FITS cards appears as a header at the start of every FITS data file, and sometimes also at other points within it, and is used to provide ancillary information which qualifies or describes the main array of data stored in the file. As such, FITS headers are prime territory for storing information about the coordinate systems associated with data held in FITS files.
In this section, we will examine how to store information in FITS
headers directly in the form of AST Objects--a process which is
supported by a specialised class of Channel called a FitsChan. Our
discussion here will turn out to be a transitional step that
emphasises the similarities between a FitsChan and a Channel
(). At the same time, it will prepare us for the
next section (), where we will examine how to
use a FitsChan to tackle some of the more difficult problems that FITS
headers can present.
AST A Library for Handling World Coordinate Systems in Astronomy