Image World Coordinate Setting Program

imwgsc is an alias for imwcs, a program which sets the world coordinate system (WCS) of a FITS or IRAF image. The WCS is the relationship between sky coordinates and image pixels and can be described in a standard way in the header of an image. The program was originally written at the University of Iowa, but has been adapted and amplified by Doug Mink at the Smithsonian Astrophysical Observatory.

imwgsc uses the Hubble Space Telescope Guide Star Catalog, which contains 25,541,952 entries, and works on about half of the 10 arcminute square images I've encountered. The GSC-ACT Catalog is a more accurate version of the same catalog, and can be invoked using imwgsca. The USNO-A2.0 catalog has enough stars to fit almost any ground-based image, and is invoked using imwua2. The 2MASS Point Source Catalog (imwtmc) and the GSC II Catalog (imwgsc2) have fewer stars than the USNO-A2.0, but they are based on positions closer to the present, i.e. 1990's rather than 1950's.

A set of image stars may be hand-matched to sky positions and used to get a WCS or set initial values for a reference catalog-based WCS (See example).

Command Line Arguments


Using SExtractor to find stars in an image

Find image WCS using HST Guide Stars as references

Find image WCS using pre-matched stars and USNO-A2.0 Stars

Last updated 19 October 2001 by Doug Mink

Telescope Data Center [WCSTools Programs]