David Berry wrote:

Just for completeness... the AST library (www.starlink.ac.uk/ast/) also
handles CD (both CDi_j and CDiiijjj) and PC matrices (both PCi_j and
PCiiijjj), and includes a parsing system (i.e. you give it an entire
header, and it sucks out the bits it needs and gives you a pointer to
an object representing all the WCS information in the header).

Since I didn't note it before, WCSTools also provides a single-call
parsing subroutine which ingests a FITS header and returns a WCS
structure or cascading WCS structures if the designated WCS depends
on others. FITS reading software is also included--my FITS experience
predates CFITSIO--so there is another single subroutien call which
returns the WCS structure(s) given a FITS or IRAF .imh file name.

-Doug Mink