WCSTools: an Image Astrometry Toolkit

Most astronomical images are now digital. Those which are taken on CCD detectors at most telescopes arrive with only rudimentary pointing information. Software tools have been written to automatically match imaged objects to source catalogs and save the relationship between pixel position and sky position in the image files in a more accurate way. This world coordinate system (WCS) is then used for a variety of purposes such as displaying sky coordinates while browsing an image, with such programs as SAOimage or SKYCAT, catalog positions of objects in an image, or listing all of the HST Guide Stars or USNO A 1.0 stars which should appear in an image. As this code can also deal with the world coordinate systems written into Space Telescope or Digitized Sky Survey data, they are tools for astronomers needing positions of objects in almost any kind of digital astronomical image.