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The gastro program determines the astrometric transformation for an
image based on the cmp/smp file.  This file contains both the table of
object data and the complete image FITS header.  Using the header
astrometric information as a starting point, gastro loads the
reference astrometry objects appropriate for the region and determines
the matching objects between the image and the reference.  These
objects are used, with iteration to improve the sample, to determine
the astrometric transformation with up to 3rd order polynomials.  

<pre>
gastro filtname.cmp
options:
  -h
  -help
  -v
  -p (photcode)
  -plot
  -maglims
  -nstars
  -fx
  -fy
  -coords (ra) (dec)
  -dump
  -mdmp
  -cdmp
  -loneos

gastro configuration variables:
OFFSET_RADIUS     - max allowed offset in gcenter
MIN_MATCHES       - min number of matched stars for linear fit
MINIMUM_RADIUS    - target matching radius in gfit iterations
MAX_ERROR         - maximum allowed error in solution
MAX_NONLINEAR     - maximum angle between axes
MAX_PRECISE       - unused?
DEFAULT_RADIUS    - unused?

ROUGH_ASTROMETRY  - source of initial astrometry terms

CCD_PC1_1         - initial guess pc1_1
CCD_PC2_2         - initial guess pc2_2
CCD_PC1_2         - initial guess pc1_2
CCD_PC2_1         - initial guess pc2_1
ASEC_PIX          - initial guess arcsec / pix

POLAR_ALIGNMENT   - provide polar alignment of telescope mount?
POLAR_AXIS_RA     - RA of telescope polar axis
POLAR_AXIS_DEC    - DEC of telescope polar axis
RA_OFFSET         - RA offset
DEC_OFFSET        - DEC offset (degenerate?)

NFIELD            - select stars from region NFIELD x detector size
NPOLYTERMS	  - number of orders to allow
MMIN              - minimum magnitude of allowed star 
ROT_ZERO          - zero of tested rotation range
dROT              - rotation step size
NROT              - number of rotation tests = 2NROT + 1
GSCFILE           - name of HST GSC table file
GSCDIR            - name of HST GSC data directory
LONEOS_REGIONS    - table of location coordinates
USNO_CDROM        - name of USNO data directory
ASTRO_REFCAT      - reference catalog format to read
CATDIR            - name of ptolemy database
PHOTCODE_FILE     - table of photcodes 
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