Name

       imwcs - Set WCS in FITS and IRAF image files

Synopsis

       imwcs [options] FITS or IRAF filename

Description

       imwcs  (pronounced im-W-C-S) is a utility for setting 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.

       imwcs  currently  works  only  on  images  where the rotation about the center is known to
       within a few degrees It  has  been  tested  extensively  only  on  images  with  near-zero
       rotation.

       A  plane-tangent  projection  (center  right  ascension  and declination, plate scale, and
       rotation angle) is fit based on matches  between  stars  in  the  image  and  stars  in  a
       reference catalog. The HST Guide Star Catalog, the USNO A 1.0, SA 1.0, or UJ Catalog, or a
       user-supplied, tab-delimited Starbase catalog may be used.

Options

       -a <angle>
              Initial rotation angle in degrees (default 0)

       -b <RA> <Dec>
              Initial center in B1950 (FK4) RA and Dec (default=RA,DEC from file)

       -c <catalog name>
              Reference  catalog  (gsc(=HST  GSC),  ua2(=USNO-A2.0),  TMC(=2MASS   Point   Source
              Catalog), gsc2(=GSC II), ub1(=USNO-B1.0), local file, etc.)

       -d <catalog name>
              Use  this  DAOFIND  output  catalog of X, Y, and magnitude instead of searching for
              stars in the image.  The format is simply white-space-separated X, Y, and  magnitue
              on a line, with # at the beginning of comment lines.

       -e     Erase image WCS keywords, getting initial WCS from command line

       -f     Write FITS output no matter what input

       -g <class>
              Guide Star Catalog class (-1=all,0,3) (default -1)

       -h <number>
              Change the maximum number of reference stars to match from 25 to

       -i <counts>
              Minimum  peak  value  for  star  in  image.   If  negative,  use -<counts> standard
              deviations as minimum.

       -j <RA> <Dec>
              Initial center in J2000 (FK5) RA and Dec (default=RA,DEC from file)

       -k <magnum>
              Use this magnitude to sort brightest catalog stars.

       -l     Reflect left<->right before rotating and fitting

       -m [<bright magnitude>] <faint magnitude>
              Limiting catalog magnitude(s) (default none, bright -2 if only faint is given)

       -n <number>
              Number of parameters to fit (1-8, or digit string). The default is 2 (RA+Dec) if <3
              stars   are   matched,   3   (RA+Dec+scale)   if   <5   stars  are  matched,  or  4
              (RA+Dec+scale+rot) if 5 or more stars are matched.  Alternatively  this  may  be  a
              list of all of the parameters to fit, in the form nnnnnn.., where 1=RA, 2=Dec, 3=RA
              scale, 4=Dec scale, 5=rotation angle, 6=Y axis rotation (CD matrix), 7=RA reference
              pixel, and 8=Dec reference pixel.

       -o <filename>
              Write  output  to  this  file;  may  be  the  same  as  input  file.   This  option
              automatically sets the -w option to write the file.

       -p <scale>
              Initial plate scale in arcsec per pixel (default 0)

       -q <option list>
              <i>terate, <r>ecenter, <s>igma clip, <p>olynomial,  <t>olerance  reduce  (half  for
              each iteration).  A number following an option repeats the option that many times.

       -r <angle>
              Rotation angle in degrees before fitting (0, 90, 180, 270) (default 0)

       -s <frac>
              Use this fraction extra stars (default 1.0)

       -t <num>
              Offset tolerance in pixels (default 20)

       -u <file>
              File of X Y RA Dec assignments for initial WCS

       -v     Verbose listing of processing intermediate results

       -w     Write  WCS to a new file (default is read-only) -x X and Y coordinates of reference
              pixel (default is image center) -y multiply image dimensions  by  this  for  search
              (default  is 1) -z Use AIPS classic projections instead of WCSLIB; use CD matrix or
              CDELT instead of polynomial solution.

Web Page

       http://tdc-www.harvard.edu/software/wcstools/imwcs/

Author

       Doug Mink, SAO (dmink@cfa.harvard.edu)