imwcs - Set WCS in FITS and IRAF image files
imwcs [options] FITS or IRAF filename
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.
- -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.
http://tdc-www.harvard.edu/software/wcstools/imwcs/
Jessica Mink, SAO (jmink@cfa.harvard.edu)