.help afiles Mar00 astcat
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NAME
afiles -- describe the standard astrometry files
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USAGE
help files

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ASTROMETRY FILES

An astrometry file is any text file containing celestial coordinate information
for a small region of the sky. A minimal astrometry file consists of a list
of celestial coordinate pairs one pair per line. Most astrometry files also
contain additional non- positional information, e.g. proper motions,
magnitudes, colors, etc.

A standard astrometry file as an astrometry file containing a standard header
describing the contents and format of the file. The astcat tasks use the
header to decode the file. Normally the astrometry file header is derived
from the parent astrometric catalog description in the catalog configuration
file. If the astrometry file header is missing one may be constructed
after the fact by setting the standard field description parameter
in the \fIacatpars\fR parameter set and running the \fIafiltcat\fR task.

A set of standard field names is reserved for describing the format of 
astrometry files. The current list of standard field names is:
id, ra, dec, era, edec, pmra, pmdec, epmra, epmdec, catsystem, equinox,
epoch, px, rv, epx, erv, mag, color, emag, ecolor, xp, yp, xc, yc, exc,
eyc, imag, and eimag. For more information about these fields type
"help acatpars".

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SAMPLE STANDARD ASTROMETRY FILE

A sample astrometry file in standard format is shown below.

.nf
# BEGIN CATALOG HEADER
#    type stext
#    nheader 1
#        csystem J2000
#    nfields 4
#        ra 1 0 d hours %12.3h
#       dec 2 0 d degrees %12.2h
#      mag1 3 0 r INDEF %4.1f
#      mag2 4 0 r INDEF %4.1f
# END CATALOG HEADER

 00:00:01.443   -0:06:57.52  13.5  15.2
 00:00:01.574   -0:05:33.26  16.1  18.0
 00:00:01.904   -0:09:48.51  18.2  19.6
 00:00:02.529   -0:04:21.53  13.4  14.4
 00:00:04.154   -0:01:56.32  17.1  18.3
 00:00:04.438   -0:05:00.03  11.4  13.5
 00:00:04.697   -0:03:24.59  16.9  17.7
 00:00:05.989   -0:02:46.36  15.1  17.6
 00:00:07.118   -0:09:03.53  19.1  19.8
 00:00:07.260   -0:06:47.95  17.0  17.7
 00:00:07.314   -0:00:22.35  15.3  16.8
 00:00:07.818   -0:02:25.90  12.2  12.4
.fi

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SAMPLE ASTROMETRY FILE

A sample headerless astrometry file is shown below where ra, dec, mag1
and mag2 are stored in columns 1 through 4 respectively.

.nf
 00:00:01.443   -0:06:57.52  13.5  15.2
 00:00:01.574   -0:05:33.26  16.1  18.0
 00:00:01.904   -0:09:48.51  18.2  19.6
 00:00:02.529   -0:04:21.53  13.4  14.4
 00:00:04.154   -0:01:56.32  17.1  18.3
 00:00:04.438   -0:05:00.03  11.4  13.5
 00:00:04.697   -0:03:24.59  16.9  17.7
 00:00:05.989   -0:02:46.36  15.1  17.6
 00:00:07.118   -0:09:03.53  19.1  19.8
 00:00:07.260   -0:06:47.95  17.0  17.7
 00:00:07.314   -0:00:22.35  15.3  16.8
 00:00:07.818   -0:02:25.90  12.2  12.4
.fi

This file can be converted to standard form with the afiltcat task as follows

.nf
cl> agetcat input output filter- ra="1 hours %12.3h" dec="2 degrees %12.2h" \
mag="1-2 INDEF %4.1f"
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or by editing in a header of the form shown in the previous section. The
lines

.nf
# BEGIN CATALOG HEADER
# END CATALOG HEADER
.fi

delimit the header. The header must contain the type, nheader, and
nfields keyword value pairs and accurate descriptions of file the format.

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SEE ALSO
help catalogs, agetcat, afiltcat, acatpars
.endhelp