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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: (radians)
double plate_centre_dec #i: (radians)
double object_ra #i: (radians)
double object_dec #i: (radians)
double xi_object #o: standard coordinate (rad)
double eta_object #o: standard coordinate (rad)
double div
begin
# Find divisor
div=(dsin(object_dec)*dsin(plate_centre_dec)+
dcos(object_dec)*dcos(plate_centre_dec)*
dcos(object_ra-plate_centre_ra))
# Compute standard coords and convert to arcsec
xi_object = dcos(object_dec)*dsin(object_ra-plate_centre_ra)*
ARCSEC_PER_RADIAN/div
eta_object = (dsin(object_dec)*dcos(plate_centre_dec)-
dcos(object_dec)*dsin(plate_centre_dec)*
dcos(object_ra-plate_centre_ra))*
ARCSEC_PER_RADIAN/div
end
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