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...Read a WCS Calibration from a Dataset

Precisely how you extract world coordinate system (WCS) information from a dataset obviously depends on what type of dataset it is. Usually, however, you should be able to obtain a set of FITS header cards which contain the WCS information (and probably much more besides). Suppose that “cards” is a pointer to a string containing a complete set of concatenated FITS header cards (such as produced by the CFITSIO function fits_hdr2str). Then proceed as follows:

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The result should be a pointer, “wcsinfo”, to a FrameSetFrameSet which contains the WCS information. This pointer can now be used to perform many useful tasks, some of which are illustrated in the following recipes.

Some datasets which do not easily yield FITS header cards may require a different approach, possibly involving use of a ChannelChannel or XmlChanXmlChan (§15) rather than a FitsChanFitsChan. In the case of the Starlink NDF data format, for example, all the above may be replaced by a single call to the function ndfGtwcssun33ndfGtwcs—see SUN/33sun33. The whole process can probably be encapsulated in a similar way for most data systems, whether they use FITS header cards or not.

For more details about reading WCS information from datasets, see §17.3 and §17.4. For a more general description of FitsChans and their use with FITS header cards, see §16 and §17. For more details about FrameSets, see §13 and §14.