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/*
*+
* Name:
* palSubet
* Purpose:
* Remove the E-terms from a pre IAU 1976 catalogue RA,Dec
* Language:
* Starlink ANSI C
* Type of Module:
* Library routine
* Invocation:
* void palSubet ( double rc, double dc, double eq,
* double *rm, double *dm );
* Arguments:
* rc = double (Given)
* RA with E-terms included (radians)
* dc = double (Given)
* Dec with E-terms included (radians)
* eq = double (Given)
* Besselian epoch of mean equator and equinox
* rm = double * (Returned)
* RA without E-terms (radians)
* dm = double * (Returned)
* Dec without E-terms (radians)
* Description:
* Remove the E-terms (elliptic component of annual aberration)
* from a pre IAU 1976 catalogue RA,Dec to give a mean place.
* Authors:
* PTW: Pat Wallace (STFC)
* TIMJ: Tim Jenness (JAC, Hawaii)
* {enter_new_authors_here}
* Notes:
* Most star positions from pre-1984 optical catalogues (or
* derived from astrometry using such stars) embody the
* E-terms. This routine converts such a position to a
* formal mean place (allowing, for example, comparison with a
* pulsar timing position).
* See Also:
* Explanatory Supplement to the Astronomical Ephemeris,
* section 2D, page 48.
* History:
* 2012-02-12(TIMJ):
* Initial version with documentation taken from Fortran SLA
* Adapted with permission from the Fortran SLALIB library.
* {enter_further_changes_here}
* Copyright:
* Copyright (C) 1995 Rutherford Appleton Laboratory
* Copyright (C) 2012 Science and Technology Facilities Council.
* All Rights Reserved.
* Licence:
* This program is free software: you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation, either
* version 3 of the License, or (at your option) any later
* version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* License along with this program. If not, see
* <http://www.gnu.org/licenses/>.
* Bugs:
* {note_any_bugs_here}
*-
*/
#include "pal.h"
#include "pal1sofa.h"
void palSubet ( double rc, double dc, double eq, double *rm, double *dm ) {
double a[3]; /* The E-terms */
double v[3];
double f;
int i;
/* Note the preference for IAU routines */
/* Retrieve the E-terms */
palEtrms( eq, a );
/* Spherical to Cartesian */
eraS2c( rc, dc, v );
/* Include the E-terms */
f = 1.0 + eraPdp( v, a );
for (i=0; i<3; i++) {
v[i] = f*v[i] - a[i];
}
/* Cartesian to spherical */
eraC2s( v, rm, dm );
/* Bring RA into conventional range */
*rm = eraAnp( *rm );
}
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