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Input/Output Facilities

AST allows you to convert any kind of Object into a stream of text which contains a full description of that Object. This text may be written out by one program and read back in by another, thus allowing the original Object to be reconstructed.

The filter which converts Objects into text and back again is itself a kind of Object, called a Channel. A Channel provides a number of options for controlling the information content of the text, such as the addition of comments for human interpretation. It is also possible to intercept the text being processed by a Channel so that it may be redirected to/from any chosen external data store, such as a text file, an astronomical dataset, or a network connection.

To further facilitate the storage of coordinate system information in astronomical datasets, a more specialised form of Channel called a FitsChan is provided. Instead of using free-format text, a FitsChan converts AST Objects to and from FITS header cards. It also allows the information to be encoded in the FITS cards in a number of ways (called encodings), so that WCS information from a variety of sources can be handled.

Further reading: For a more complete description of Channels see [*] and for FitsChans see [*] and [*]. Also see the Channel and FitsChan entries in [*] and the Encoding entry in [*].



next up previous
Next: Producing Graphical Output
Up: Overview of AST Concepts
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AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
30th April 2003
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2003 Central Laboratory of the Research Councils