WCSLIB is a set of C library routines that implements the World
Coordinate System (WCS) standard in FITS (Flexible Image Transport
System). It comes with support for FORTRAN via a set of wrapper
functions. It also includes a general curvilinear axis drawing
routine, PGSBOX, for PGPLOT. Another included utility program is
HPXcvt, which is used to convert 1D HEALPix pixelization data stored
in a variety of forms in FITS into a 2D primary image array with HPX
or XPH coordinate representation.

Usage with gcc compiler: use "-lwcs" command line argument for linking
at compile time.