Astronomers often need to relate positions on an image of the sky to
positions on the real sky to identify catalogued objects in images,
tell other people where to look to find an identified object, or
to compute motions of planets, satellites, asteroids, or comets.
WCSTools is a package of programs and a library of utility
subroutines for setting and using the
world coordinate systems (WCS)
in the headers of the most common astronomical image formats,
to relate image pixels to sky coordinates.
This software is all written in very portable C, so it should compile
and run on any computer with a C compiler.
The current version is 3.9.5 (Older Versions are here)
Some subroutines in the
library have been adapted and amplified from software originally written
by Elwood Downey of the
University of Iowa Automated Telescope Facility,
Bill Cotton of the U.S. NRAO,
Mark Calabretta of the Australian
and Pat Wallace of the
UK Starlink Project.
Others are translated from the Fortran code I wrote to support the
This software was originally inspired by the impending standardization
of WCS keywords in FITS as discussed at the 1994 ADASS Conference. The
subroutines to translate between sky and image coordinates came first,
then the utilities to use them, and then the programs to search catalogs
and fit a world coordinate systems to images.