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Diffstat (limited to 'ast/erfa/atioq.c')
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diff --git a/ast/erfa/atioq.c b/ast/erfa/atioq.c new file mode 100644 index 0000000..be3dfbc --- /dev/null +++ b/ast/erfa/atioq.c @@ -0,0 +1,244 @@ +#include "erfa.h" + +void eraAtioq(double ri, double di, eraASTROM *astrom, + double *aob, double *zob, + double *hob, double *dob, double *rob) +/* +** - - - - - - - - - +** e r a A t i o q +** - - - - - - - - - +** +** Quick CIRS to observed place transformation. +** +** Use of this function is appropriate when efficiency is important and +** where many star positions are all to be transformed for one date. +** The star-independent astrometry parameters can be obtained by +** calling eraApio[13] or eraApco[13]. +** +** Given: +** ri double CIRS right ascension +** di double CIRS declination +** 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) +** +** Returned: +** aob double* observed azimuth (radians: N=0,E=90) +** zob double* observed zenith distance (radians) +** hob double* observed hour angle (radians) +** dob double* observed declination (radians) +** rob double* observed right ascension (CIO-based, radians) +** +** Notes: +** +** 1) This function returns zenith distance rather than altitude in +** order to reflect the fact that no allowance is made for +** depression of the horizon. +** +** 2) The accuracy of the result is limited by the corrections for +** refraction, which use a simple A*tan(z) + B*tan^3(z) model. +** Providing the meteorological parameters are known accurately and +** there are no gross local effects, the predicted observed +** coordinates should be within 0.05 arcsec (optical) or 1 arcsec +** (radio) for a zenith distance of less than 70 degrees, better +** than 30 arcsec (optical or radio) at 85 degrees and better +** than 20 arcmin (optical) or 30 arcmin (radio) at the horizon. +** +** Without refraction, the complementary functions eraAtioq and +** eraAtoiq are self-consistent to better than 1 microarcsecond all +** over the celestial sphere. With refraction included, consistency +** falls off at high zenith distances, but is still better than +** 0.05 arcsec at 85 degrees. +** +** 3) 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. +** +** 4) The CIRS RA,Dec is obtained from a star catalog mean place by +** allowing for space motion, parallax, the Sun's gravitational lens +** effect, annual aberration and precession-nutation. For star +** positions in the ICRS, these effects can be applied by means of +** the eraAtci13 (etc.) functions. Starting from classical "mean +** place" systems, additional transformations will be needed first. +** +** 5) "Observed" Az,El means the position that would be seen by a +** perfect geodetically aligned theodolite. This is obtained from +** the CIRS RA,Dec by allowing for Earth orientation and diurnal +** aberration, rotating from equator to horizon coordinates, and +** then adjusting for refraction. The HA,Dec is obtained by +** rotating back into equatorial coordinates, and is the position +** that would be seen by a perfect equatorial with its polar axis +** aligned to the Earth's axis of rotation. Finally, the RA is +** obtained by subtracting the HA from the local ERA. +** +** 6) The star-independent CIRS-to-observed-place parameters in ASTROM +** may be computed with eraApio[13] or eraApco[13]. If nothing has +** changed significantly except the time, eraAper[13] may be used to +** perform the requisite adjustment to the astrom structure. +** +** Called: +** eraS2c spherical coordinates to unit vector +** eraC2s p-vector to spherical +** eraAnp normalize angle into range 0 to 2pi +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Minimum cos(alt) and sin(alt) for refraction purposes */ + const double CELMIN = 1e-6; + const double SELMIN = 0.05; + + double v[3], x, y, z, xhd, yhd, zhd, f, xhdt, yhdt, zhdt, + xaet, yaet, zaet, azobs, r, tz, w, del, cosdel, + xaeo, yaeo, zaeo, zdobs, hmobs, dcobs, raobs; + +/*--------------------------------------------------------------------*/ + +/* CIRS RA,Dec to Cartesian -HA,Dec. */ + eraS2c(ri-astrom->eral, di, v); + x = v[0]; + y = v[1]; + z = v[2]; + +/* Polar motion. */ + xhd = x + astrom->xpl*z; + yhd = y - astrom->ypl*z; + zhd = z - astrom->xpl*x + astrom->ypl*y; + +/* Diurnal aberration. */ + f = ( 1.0 - astrom->diurab*yhd ); + xhdt = f * xhd; + yhdt = f * ( yhd + astrom->diurab ); + zhdt = f * zhd; + +/* Cartesian -HA,Dec to Cartesian Az,El (S=0,E=90). */ + xaet = astrom->sphi*xhdt - astrom->cphi*zhdt; + yaet = yhdt; + zaet = astrom->cphi*xhdt + astrom->sphi*zhdt; + +/* Azimuth (N=0,E=90). */ + azobs = ( xaet != 0.0 || yaet != 0.0 ) ? atan2(yaet,-xaet) : 0.0; + +/* ---------- */ +/* Refraction */ +/* ---------- */ + +/* Cosine and sine of altitude, with precautions. */ + r = sqrt(xaet*xaet + yaet*yaet); + r = r > CELMIN ? r : CELMIN; + z = zaet > SELMIN ? zaet : SELMIN; + +/* A*tan(z)+B*tan^3(z) model, with Newton-Raphson correction. */ + tz = r/z; + w = astrom->refb*tz*tz; + del = ( astrom->refa + w ) * tz / + ( 1.0 + ( astrom->refa + 3.0*w ) / ( z*z ) ); + +/* Apply the change, giving observed vector. */ + cosdel = 1.0 - del*del/2.0; + f = cosdel - del*z/r; + xaeo = xaet*f; + yaeo = yaet*f; + zaeo = cosdel*zaet + del*r; + +/* Observed ZD. */ + zdobs = atan2(sqrt(xaeo*xaeo+yaeo*yaeo), zaeo); + +/* Az/El vector to HA,Dec vector (both right-handed). */ + v[0] = astrom->sphi*xaeo + astrom->cphi*zaeo; + v[1] = yaeo; + v[2] = - astrom->cphi*xaeo + astrom->sphi*zaeo; + +/* To spherical -HA,Dec. */ + eraC2s ( v, &hmobs, &dcobs ); + +/* Right ascension (with respect to CIO). */ + raobs = astrom->eral + hmobs; + +/* Return the results. */ + *aob = eraAnp(azobs); + *zob = zdobs; + *hob = -hmobs; + *dob = dcobs; + *rob = eraAnp(raobs); + +/* 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. +** +*/ |