Install wcstools with Homebrew, apt, dnf, MacPorts

Project links

• Homepage
• Upstream docs
• Package manager page

Commands and aliases

• addpix
• bincat
• char2sp
• conpix
• cphead
• crlf
• delhead
• delwcs
• edhead
• filename
• fileroot
• filext
• fixpix
• getcol
• getdate
• getfits
• gethead
• getpix
• gettab
• htmlsp
• i2f
• imcat
• imextract
• imfill
• imhead
• immatch
• imresize
• imrot
• imsize
• imsmooth
• imstack
• imstar

Project history

The published lineage begins in the mid-1990s. Douglas J. Mink's 1996 ADASS paper explains that after WCS support was added to SAOimage and then to SAOtng and SkyCat, astronomers still lacked WCS headers for much ground-based optical data. Mink adapted Elwood Downey's University of Iowa SETWCS approach into IMWCS and, as the software was generalized for more image types and reference catalogs, a wider suite of portable WCS utilities and subroutines emerged.

By the 1998 ADASS paper, WCSTools had become an image astrometry toolkit rather than a single fitting program. The package provided both modular subroutines and simple programs, read and wrote FITS and IRAF .imh images, supported many map projections used in FITS WCS work, and was explicitly designed to be easy to call from scripts.

The 2001 ADASS paper on WCSTools 3.0 described five years of use in image astrometry and noted that the package had grown alongside new reference catalogs such as GSC-ACT, 2MASS, and GSC II. The current upstream README identifies version 3.9.7, released April 26, 2022, as a mature continuation of the same SAO codebase maintained by Jessica Mink with contributions and algorithms from astronomy software specialists at institutions including CSIRO, NRAO, STScI, IPAC, NOAO, and others.

Adoption history

WCSTools became important partly because its subroutines were adopted by astronomical image browsers. The 1998 paper says SAOtng, its successor, and SkyCat used WCSTools subroutines, while the ASP abstract also lists SAOimage, SkyCat, and SAOtng as users of the library for displaying sky coordinates while browsing images.

Its adoption pattern is classic scientific Unix software: not a broad consumer tool, but a durable utility layer for observatories, archives, and astronomers who need repeatable FITS/IRAF header manipulation, catalog searches, and coordinate conversion inside scripts.

How it is used

Typical usage starts with existing FITS or IRAF images. imwcs can match image stars against reference catalogs and fit a WCS into the image header; xy2sky and sky2xy translate between pixel coordinates and sky coordinates; scat and imcat query source catalogs; gethead, sethead, edhead, and related tools inspect or edit FITS and IRAF metadata.

The toolkit is especially useful when older or ground-based images lack complete WCS headers. In that context, WCSTools can extract image stars, compare them to reference catalogs or Digitized Sky Survey fields, write WCS keywords, and then let downstream programs treat image positions as sky positions.

Why package nerds care

WCSTools is significant because it preserves a Unix-style astronomy workflow around FITS WCS: small executables, text-friendly output, and direct interoperability with shell scripts. For package maintainers, it is a good example of scientific software whose value comes from decades of domain compatibility rather than a modern repository or dependency graph.

It also documents the pre-Astropy, pre-service era of astronomical tooling, where command-line C utilities, IRAF compatibility, SAOimage-family viewers, and catalog CD-ROMs or web services were stitched together into practical astrometry pipelines.

Timeline

• 1996: Mink presents the IMWCS-focused WCSTools work at ADASS VI, describing the adaptation from SETWCS and the development of portable WCS utilities.
• 1998: Mink presents WCSTools as a broader image astrometry toolkit at ADASS VIII, emphasizing subroutines, command-line programs, scriptability, FITS/IRAF support, and image-browser integration.
• 2001-2002: The WCSTools 3.0 paper describes five years of image astrometry use and catalog-search expansion, including support for newer large catalogs.
• 2022-04-26: The upstream README lists WCSTools 3.9.7 and a detailed set of recent fixes and new utility behavior.

Related projects

• WCSTools is historically connected to SAOimage, SAOtng, SkyCat, FITS, IRAF, the Digitized Sky Survey, HST Guide Star Catalog, USNO catalogs, 2MASS, WCSLIB, Astropy WCS tooling, and other astrometry packages such as SExtractor, SCAMP, and Astrometry.net.

Sources

• http://tdc-www.harvard.edu/software/wcstools/publications/wcstools.adass96.html
• http://tdc-www.harvard.edu/software/wcstools/publications/wcstools.adass98.html
• http://tdc-www.harvard.edu/software/wcstools/wcstools.readme.html
• https://ui.adsabs.harvard.edu/abs/2011ascl.soft09015M/abstract
• https://www.aspbooks.org/a/volumes/article_details/?paper_id=17573
• https://www.atnf.csiro.au/computing/software/wcs/wcslib/software.html