#!/bin/sh
#
##1 fk54 - Convert the ra and dec columns of an starbase data table from FK5 to FK4.
#
#	fk54 < file rcol dcol
#
# DESCRIPTION
# Convert a J2000.0 FK5 star position from the starbase data table 
# read from the standard input to B1950.0 FK4 assuming
# zero proper motion and parallax.
#
# Star positions are converted from the new, IAU 1976,
# FK5, Fricke system to the old, Bessel-Newcomb, FK4 system.
#
# PARAMETERS
#  *rcol	The column name of the ra column defaults to "ra".  The
#		column should contain RA coordinate values in hours.
#  *dcol	The column name of the dec column defaults to "dec".  The
#		column should contain Dec coordinate values in degrees.
#  *bepoch	The converted position in the B1950
#		reference frame but at Besselian epoch bepoch.  For
#		comparison with catalogues the bepoch argument will
#		frequently be 1950.0 and is the default.
#
# SEE ALSO
#   *<@fk54.src@>	Source text of #fk54.
#   *<#@slalink.1#>	programs available with the slalink extensions to #tawk.
#   *<#@slalink.4#>	functions available with the slalink extensions to #tawk.
#   *<#@precess#>	Precess the ra and dec columns from one equinox to another.
#   *<#@fk45#>		Convert the ra and dec columns of an starbase data table from FK4 to FK5.
#

export TABLEFUNCTIONS
TABLEFUNCTIONS=""

 while [ $# -ge 1 ] ; do
  case $1 in 
   -i) shift; ifile=$1					;;
   -o) shift; ofile=$1					;;
   -*) echo "fk54: unknown option"; exit 1	;;
    *) argv="$argv $1"					;;
  esac
  shift
 done

 if [ "$ifile" != "" ] ; then
	exec < $ifile
 fi

 if [ "$ofile" != "" ] ; then
	exec > $ofile
 fi

table -p '
BEGIN {
	Init = 0

	rcol 	= "ra"
	dcol 	= "dec"
	bepoch	=  1950

	paramcheck("fk54", "rcol|dcol|bepoch")
}
!Init {	__r = table_colnum(rcol)
	__d = table_colnum(dcol)

	if ( !__r )	printf("fk54: no column \"%s\".\n", rcol) > "/dev/stderr"
	if ( !__d )	printf("fk54: no column \"%s\".\n", dcol) > "/dev/stderr"
	if ( !__r || !__d ) {
		exit 1
	}

	Init = 1
}
{	[ $__r, $__d ] = fk54($__r, $__d, bepoch); print }

include(../tablefun/paramcheck)
include(../tablefun/table_colnum)

 ' $argv