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+#include "erfa.h"
+
+void eraApco(double date1, double date2,
+ double ebpv[2][3], double ehp[3],
+ double x, double y, double s, double theta,
+ double elong, double phi, double hm,
+ double xp, double yp, double sp,
+ double refa, double refb,
+ eraASTROM *astrom)
+/*
+** - - - - - - - -
+** e r a A p c o
+** - - - - - - - -
+**
+** For a terrestrial observer, prepare star-independent astrometry
+** parameters for transformations between ICRS and observed
+** coordinates. The caller supplies the Earth ephemeris, the Earth
+** rotation information and the refraction constants as well as the
+** site coordinates.
+**
+** Given:
+** date1 double TDB as a 2-part...
+** date2 double ...Julian Date (Note 1)
+** ebpv double[2][3] Earth barycentric PV (au, au/day, Note 2)
+** ehp double[3] Earth heliocentric P (au, Note 2)
+** x,y double CIP X,Y (components of unit vector)
+** s double the CIO locator s (radians)
+** theta double Earth rotation angle (radians)
+** elong double longitude (radians, east +ve, Note 3)
+** phi double latitude (geodetic, radians, Note 3)
+** hm double height above ellipsoid (m, geodetic, Note 3)
+** xp,yp double polar motion coordinates (radians, Note 4)
+** sp double the TIO locator s' (radians, Note 4)
+** refa double refraction constant A (radians, Note 5)
+** refb double refraction constant B (radians, Note 5)
+**
+** Returned:
+** astrom eraASTROM* star-independent astrometry parameters:
+** pmt double PM time interval (SSB, Julian years)
+** eb double[3] SSB to observer (vector, au)
+** eh double[3] Sun to observer (unit vector)
+** em double distance from Sun to observer (au)
+** v double[3] barycentric observer velocity (vector, c)
+** bm1 double sqrt(1-|v|^2): reciprocal of Lorenz factor
+** bpn double[3][3] bias-precession-nutation matrix
+** along double longitude + s' (radians)
+** xpl double polar motion xp wrt local meridian (radians)
+** ypl double polar motion yp wrt local meridian (radians)
+** sphi double sine of geodetic latitude
+** cphi double cosine of geodetic latitude
+** diurab double magnitude of diurnal aberration vector
+** eral double "local" Earth rotation angle (radians)
+** refa double refraction constant A (radians)
+** refb double refraction constant B (radians)
+**
+** Notes:
+**
+** 1) The TDB date date1+date2 is a Julian Date, apportioned in any
+** convenient way between the two arguments. For example,
+** JD(TDB)=2450123.7 could be expressed in any of these ways, among
+** others:
+**
+** date1 date2
+**
+** 2450123.7 0.0 (JD method)
+** 2451545.0 -1421.3 (J2000 method)
+** 2400000.5 50123.2 (MJD method)
+** 2450123.5 0.2 (date & time method)
+**
+** The JD method is the most natural and convenient to use in cases
+** where the loss of several decimal digits of resolution is
+** acceptable. The J2000 method is best matched to the way the
+** argument is handled internally and will deliver the optimum
+** resolution. The MJD method and the date & time methods are both
+** good compromises between resolution and convenience. For most
+** applications of this function the choice will not be at all
+** critical.
+**
+** TT can be used instead of TDB without any significant impact on
+** accuracy.
+**
+** 2) The vectors eb, eh, and all the astrom vectors, are with respect
+** to BCRS axes.
+**
+** 3) The geographical coordinates are with respect to the ERFA_WGS84
+** reference ellipsoid. TAKE CARE WITH THE LONGITUDE SIGN
+** CONVENTION: the longitude required by the present function is
+** right-handed, i.e. east-positive, in accordance with geographical
+** convention.
+**
+** 4) xp and yp are the coordinates (in radians) of the Celestial
+** Intermediate Pole with respect to the International Terrestrial
+** Reference System (see IERS Conventions), measured along the
+** meridians 0 and 90 deg west respectively. sp is the TIO locator
+** s', in radians, which positions the Terrestrial Intermediate
+** Origin on the equator. For many applications, xp, yp and
+** (especially) sp can be set to zero.
+**
+** Internally, the polar motion is stored in a form rotated onto the
+** local meridian.
+**
+** 5) The refraction constants refa and refb are for use in a
+** dZ = A*tan(Z)+B*tan^3(Z) model, where Z is the observed
+** (i.e. refracted) zenith distance and dZ is the amount of
+** refraction.
+**
+** 6) It is advisable to take great care with units, as even unlikely
+** values of the input parameters are accepted and processed in
+** accordance with the models used.
+**
+** 7) In cases where the caller does not wish to provide the Earth
+** Ephemeris, the Earth rotation information and refraction
+** constants, the function eraApco13 can be used instead of the
+** present function. This starts from UTC and weather readings etc.
+** and computes suitable values using other ERFA functions.
+**
+** 8) 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.
+**
+** 9) The context structure astrom produced by this function is used by
+** eraAtioq, eraAtoiq, eraAtciq* and eraAticq*.
+**
+** Called:
+** eraAper astrometry parameters: update ERA
+** eraC2ixys celestial-to-intermediate matrix, given X,Y and s
+** eraPvtob position/velocity of terrestrial station
+** eraTrxpv product of transpose of r-matrix and pv-vector
+** eraApcs astrometry parameters, ICRS-GCRS, space observer
+** eraCr copy r-matrix
+**
+** Copyright (C) 2013-2016, NumFOCUS Foundation.
+** Derived, with permission, from the SOFA library. See notes at end of file.
+*/
+{
+ double sl, cl, r[3][3], pvc[2][3], pv[2][3];
+
+
+/* Longitude with adjustment for TIO locator s'. */
+ astrom->along = elong + sp;
+
+/* Polar motion, rotated onto the local meridian. */
+ sl = sin(astrom->along);
+ cl = cos(astrom->along);
+ astrom->xpl = xp*cl - yp*sl;
+ astrom->ypl = xp*sl + yp*cl;
+
+/* Functions of latitude. */
+ astrom->sphi = sin(phi);
+ astrom->cphi = cos(phi);
+
+/* Refraction constants. */
+ astrom->refa = refa;
+ astrom->refb = refb;
+
+/* Local Earth rotation angle. */
+ eraAper(theta, astrom);
+
+/* Disable the (redundant) diurnal aberration step. */
+ astrom->diurab = 0.0;
+
+/* CIO based BPN matrix. */
+ eraC2ixys(x, y, s, r);
+
+/* Observer's geocentric position and velocity (m, m/s, CIRS). */
+ eraPvtob(elong, phi, hm, xp, yp, sp, theta, pvc);
+
+/* Rotate into GCRS. */
+ eraTrxpv(r, pvc, pv);
+
+/* ICRS <-> GCRS parameters. */
+ eraApcs(date1, date2, pv, ebpv, ehp, astrom);
+
+/* Store the CIO based BPN matrix. */
+ eraCr(r, astrom->bpn );
+
+/* Finished. */
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** Copyright (C) 2013-2016, 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.
+**
+*/