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+#include "erfa.h"
+
+void eraAper(double theta, eraASTROM *astrom)
+/*
+** - - - - - - - -
+** e r a A p e r
+** - - - - - - - -
+**
+** In the star-independent astrometry parameters, update only the
+** Earth rotation angle, supplied by the caller explicitly.
+**
+** Given:
+** theta double Earth rotation angle (radians, Note 2)
+** astrom eraASTROM* star-independent astrometry parameters:
+** pmt double not used
+** eb double[3] not used
+** eh double[3] not used
+** em double not used
+** v double[3] not used
+** bm1 double not used
+** bpn double[3][3] not used
+** along double longitude + s' (radians)
+** xpl double not used
+** ypl double not used
+** sphi double not used
+** cphi double not used
+** diurab double not used
+** eral double not used
+** refa double not used
+** refb double not used
+**
+** Returned:
+** astrom eraASTROM* star-independent astrometry parameters:
+** pmt double unchanged
+** eb double[3] unchanged
+** eh double[3] unchanged
+** em double unchanged
+** v double[3] unchanged
+** bm1 double unchanged
+** bpn double[3][3] unchanged
+** along double unchanged
+** xpl double unchanged
+** ypl double unchanged
+** sphi double unchanged
+** cphi double unchanged
+** diurab double unchanged
+** eral double "local" Earth rotation angle (radians)
+** refa double unchanged
+** refb double unchanged
+**
+** Notes:
+**
+** 1) This function exists to enable sidereal-tracking applications to
+** avoid wasteful recomputation of the bulk of the astrometry
+** parameters: only the Earth rotation is updated.
+**
+** 2) For targets expressed as equinox based positions, such as
+** classical geocentric apparent (RA,Dec), the supplied theta can be
+** Greenwich apparent sidereal time rather than Earth rotation
+** angle.
+**
+** 3) The function eraAper13 can be used instead of the present
+** function, and starts from UT1 rather than ERA itself.
+**
+** 4) This is one of several functions that inserts into the astrom
+** structure star-independent parameters needed for the chain of
+** astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.
+**
+** The various functions support different classes of observer and
+** portions of the transformation chain:
+**
+** functions observer transformation
+**
+** eraApcg eraApcg13 geocentric ICRS <-> GCRS
+** eraApci eraApci13 terrestrial ICRS <-> CIRS
+** eraApco eraApco13 terrestrial ICRS <-> observed
+** eraApcs eraApcs13 space ICRS <-> GCRS
+** eraAper eraAper13 terrestrial update Earth rotation
+** eraApio eraApio13 terrestrial CIRS <-> observed
+**
+** Those with names ending in "13" use contemporary ERFA models to
+** compute the various ephemerides. The others accept ephemerides
+** supplied by the caller.
+**
+** The transformation from ICRS to GCRS covers space motion,
+** parallax, light deflection, and aberration. From GCRS to CIRS
+** comprises frame bias and precession-nutation. From CIRS to
+** observed takes account of Earth rotation, polar motion, diurnal
+** aberration and parallax (unless subsumed into the ICRS <-> GCRS
+** transformation), and atmospheric refraction.
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** Derived, with permission, from the SOFA library. See notes at end of file.
+*/
+{
+ astrom->eral = theta + astrom->along;
+
+/* Finished. */
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** Copyright (C) 2013-2014, NumFOCUS Foundation.
+** All rights reserved.
+**
+** This library is derived, with permission, from the International
+** Astronomical Union's "Standards of Fundamental Astronomy" library,
+** available from http://www.iausofa.org.
+**
+** The ERFA version is intended to retain identical functionality to
+** the SOFA library, but made distinct through different function and
+** file names, as set out in the SOFA license conditions. The SOFA
+** original has a role as a reference standard for the IAU and IERS,
+** and consequently redistribution is permitted only in its unaltered
+** state. The ERFA version is not subject to this restriction and
+** therefore can be included in distributions which do not support the
+** concept of "read only" software.
+**
+** Although the intent is to replicate the SOFA API (other than
+** replacement of prefix names) and results (with the exception of
+** bugs; any that are discovered will be fixed), SOFA is not
+** responsible for any errors found in this version of the library.
+**
+** If you wish to acknowledge the SOFA heritage, please acknowledge
+** that you are using a library derived from SOFA, rather than SOFA
+** itself.
+**
+**
+** TERMS AND CONDITIONS
+**
+** Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions
+** are met:
+**
+** 1 Redistributions of source code must retain the above copyright
+** notice, this list of conditions and the following disclaimer.
+**
+** 2 Redistributions in binary form must reproduce the above copyright
+** notice, this list of conditions and the following disclaimer in
+** the documentation and/or other materials provided with the
+** distribution.
+**
+** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
+** the International Astronomical Union nor the names of its
+** contributors may be used to endorse or promote products derived
+** from this software without specific prior written permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+** POSSIBILITY OF SUCH DAMAGE.
+**
+*/