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# This routine was copied from the stsdas$pkg/analysis/gasp/gasplib/
# directory. See stsdas$copyright.stsdas for copyright restrictions.
#
define ARCSEC_PER_RADIAN 206264.8062470964d0
# TREQST -- Procedure to convert RA and Dec to standard coordinates
# given the plate centre.
procedure treqst (plate_centre_ra, plate_centre_dec, object_ra, object_dec,
xi_object, eta_object)
double plate_centre_ra #I plate ra center (radians)
double plate_centre_dec #I plate dec center (radians)
double object_ra #I object ra center (radians)
double object_dec #I object dec center (radians)
double xi_object #O object xi standard coordinate (arcsecs)
double eta_object #O object eta standard coordinate (arcsecs)
#double div
double ra, cosra, sinra, cosdec, sindec, cosd0, sind0, cosdist
begin
ra = object_ra - plate_centre_ra
cosra = cos (ra)
sinra = sin (ra)
cosdec = cos (object_dec)
sindec = sin (object_dec)
cosd0 = cos (plate_centre_dec)
sind0 = sin (plate_centre_dec)
cosdist = sindec * sind0 + cosdec * cosd0 * cosra
xi_object = cosdec * sinra * ARCSEC_PER_RADIAN / cosdist
eta_object = (sindec * cosd0 - cosdec * sind0 * cosra) *
ARCSEC_PER_RADIAN / cosdist
# # Find the divisor.
# div = (sin(object_dec) * sin(plate_centre_dec) +
# cos(object_dec) * cos(plate_centre_dec) *
# cos(object_ra -plate_centre_ra))
#
# # Compute standard coords and convert to arcsec
# xi_object = cos(object_dec) * sin(object_ra-plate_centre_ra) *
# ARCSEC_PER_RADIAN/div
# eta_object = (sin(object_dec) * cos(plate_centre_dec) -
# cos(object_dec) * dsin(plate_centre_dec) *
# cos(object_ra - plate_centre_ra)) *
# ARCSEC_PER_RADIAN/div
end
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