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Diffstat (limited to 'ast/erfa/apcs.c')
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diff --git a/ast/erfa/apcs.c b/ast/erfa/apcs.c new file mode 100644 index 0000000..0a34f14 --- /dev/null +++ b/ast/erfa/apcs.c @@ -0,0 +1,233 @@ +#include "erfa.h" + +void eraApcs(double date1, double date2, double pv[2][3], + double ebpv[2][3], double ehp[3], + eraASTROM *astrom) +/* +** - - - - - - - - +** e r a A p c s +** - - - - - - - - +** +** For an observer whose geocentric position and velocity are known, +** prepare star-independent astrometry parameters for transformations +** between ICRS and GCRS. The Earth ephemeris is supplied by the +** caller. +** +** The parameters produced by this function are required in the space +** motion, parallax, light deflection and aberration parts of the +** astrometric transformation chain. +** +** Given: +** date1 double TDB as a 2-part... +** date2 double ...Julian Date (Note 1) +** pv double[2][3] observer's geocentric pos/vel (m, m/s) +** ebpv double[2][3] Earth barycentric PV (au, au/day) +** ehp double[3] Earth heliocentric P (au) +** +** 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 unchanged +** xpl double unchanged +** ypl double unchanged +** sphi double unchanged +** cphi double unchanged +** diurab double unchanged +** eral double unchanged +** refa double unchanged +** refb double unchanged +** +** 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) All the vectors are with respect to BCRS axes. +** +** 3) Providing separate arguments for (i) the observer's geocentric +** position and velocity and (ii) the Earth ephemeris is done for +** convenience in the geocentric, terrestrial and Earth orbit cases. +** For deep space applications it maybe more convenient to specify +** zero geocentric position and velocity and to supply the +** observer's position and velocity information directly instead of +** with respect to the Earth. However, note the different units: +** m and m/s for the geocentric vectors, au and au/day for the +** heliocentric and barycentric vectors. +** +** 4) In cases where the caller does not wish to provide the Earth +** ephemeris, the function eraApcs13 can be used instead of the +** present function. This computes the Earth ephemeris using the +** ERFA function eraEpv00. +** +** 5) 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. +** +** 6) The context structure astrom produced by this function is used by +** eraAtciq* and eraAticq*. +** +** Called: +** eraCp copy p-vector +** eraPm modulus of p-vector +** eraPn decompose p-vector into modulus and direction +** eraIr initialize r-matrix to identity +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* au/d to m/s */ + const double AUDMS = ERFA_DAU/ERFA_DAYSEC; + +/* Light time for 1 AU (day) */ + const double CR = ERFA_AULT/ERFA_DAYSEC; + + int i; + double dp, dv, pb[3], vb[3], ph[3], v2, w; + + +/* Time since reference epoch, years (for proper motion calculation). */ + astrom->pmt = ( (date1 - ERFA_DJ00) + date2 ) / ERFA_DJY; + +/* Adjust Earth ephemeris to observer. */ + for (i = 0; i < 3; i++) { + dp = pv[0][i] / ERFA_DAU; + dv = pv[1][i] / AUDMS; + pb[i] = ebpv[0][i] + dp; + vb[i] = ebpv[1][i] + dv; + ph[i] = ehp[i] + dp; + } + +/* Barycentric position of observer (au). */ + eraCp(pb, astrom->eb); + +/* Heliocentric direction and distance (unit vector and au). */ + eraPn(ph, &astrom->em, astrom->eh); + +/* Barycentric vel. in units of c, and reciprocal of Lorenz factor. */ + v2 = 0.0; + for (i = 0; i < 3; i++) { + w = vb[i] * CR; + astrom->v[i] = w; + v2 += w*w; + } + astrom->bm1 = sqrt(1.0 - v2); + +/* Reset the NPB matrix. */ + eraIr(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. +** +*/ |