285 lines
11 KiB
C
285 lines
11 KiB
C
#include "sofa.h"
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void iauAtioq(double ri, double di, iauASTROM *astrom,
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double *aob, double *zob,
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double *hob, double *dob, double *rob)
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/*
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** - - - - - - - - -
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** i a u A t i o q
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** - - - - - - - - -
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**
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** Quick CIRS to observed place transformation.
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**
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** Use of this function is appropriate when efficiency is important and
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** where many star positions are all to be transformed for one date.
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** The star-independent astrometry parameters can be obtained by
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** calling iauApio[13] or iauApco[13].
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**
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** This function is part of the International Astronomical Union's
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** SOFA (Standards of Fundamental Astronomy) software collection.
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**
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** Status: support function.
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**
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** Given:
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** ri double CIRS right ascension
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** di double CIRS declination
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** astrom iauASTROM* star-independent astrometry parameters:
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** pmt double PM time interval (SSB, Julian years)
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** eb double[3] SSB to observer (vector, au)
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** eh double[3] Sun to observer (unit vector)
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** em double distance from Sun to observer (au)
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** v double[3] barycentric observer velocity (vector, c)
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** bm1 double sqrt(1-|v|^2): reciprocal of Lorenz factor
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** bpn double[3][3] bias-precession-nutation matrix
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** along double longitude + s' (radians)
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** xpl double polar motion xp wrt local meridian (radians)
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** ypl double polar motion yp wrt local meridian (radians)
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** sphi double sine of geodetic latitude
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** cphi double cosine of geodetic latitude
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** diurab double magnitude of diurnal aberration vector
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** eral double "local" Earth rotation angle (radians)
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** refa double refraction constant A (radians)
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** refb double refraction constant B (radians)
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**
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** Returned:
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** aob double* observed azimuth (radians: N=0,E=90)
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** zob double* observed zenith distance (radians)
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** hob double* observed hour angle (radians)
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** dob double* observed declination (radians)
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** rob double* observed right ascension (CIO-based, radians)
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**
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** Notes:
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**
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** 1) This function returns zenith distance rather than altitude in
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** order to reflect the fact that no allowance is made for
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** depression of the horizon.
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**
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** 2) The accuracy of the result is limited by the corrections for
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** refraction, which use a simple A*tan(z) + B*tan^3(z) model.
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** Providing the meteorological parameters are known accurately and
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** there are no gross local effects, the predicted observed
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** coordinates should be within 0.05 arcsec (optical) or 1 arcsec
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** (radio) for a zenith distance of less than 70 degrees, better
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** than 30 arcsec (optical or radio) at 85 degrees and better
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** than 20 arcmin (optical) or 30 arcmin (radio) at the horizon.
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**
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** Without refraction, the complementary functions iauAtioq and
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** iauAtoiq are self-consistent to better than 1 microarcsecond all
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** over the celestial sphere. With refraction included, consistency
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** falls off at high zenith distances, but is still better than
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** 0.05 arcsec at 85 degrees.
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**
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** 3) It is advisable to take great care with units, as even unlikely
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** values of the input parameters are accepted and processed in
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** accordance with the models used.
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**
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** 4) The CIRS RA,Dec is obtained from a star catalog mean place by
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** allowing for space motion, parallax, the Sun's gravitational lens
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** effect, annual aberration and precession-nutation. For star
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** positions in the ICRS, these effects can be applied by means of
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** the iauAtci13 (etc.) functions. Starting from classical "mean
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** place" systems, additional transformations will be needed first.
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**
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** 5) "Observed" Az,El means the position that would be seen by a
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** perfect geodetically aligned theodolite. This is obtained from
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** the CIRS RA,Dec by allowing for Earth orientation and diurnal
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** aberration, rotating from equator to horizon coordinates, and
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** then adjusting for refraction. The HA,Dec is obtained by
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** rotating back into equatorial coordinates, and is the position
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** that would be seen by a perfect equatorial with its polar axis
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** aligned to the Earth's axis of rotation. Finally, the RA is
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** obtained by subtracting the HA from the local ERA.
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**
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** 6) The star-independent CIRS-to-observed-place parameters in ASTROM
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** may be computed with iauApio[13] or iauApco[13]. If nothing has
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** changed significantly except the time, iauAper[13] may be used to
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** perform the requisite adjustment to the astrom structure.
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**
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** Called:
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** iauS2c spherical coordinates to unit vector
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** iauC2s p-vector to spherical
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** iauAnp normalize angle into range 0 to 2pi
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**
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** This revision: 2016 March 9
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**
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** SOFA release 2020-07-21
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**
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** Copyright (C) 2020 IAU SOFA Board. See notes at end.
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*/
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{
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/* Minimum cos(alt) and sin(alt) for refraction purposes */
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const double CELMIN = 1e-6;
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const double SELMIN = 0.05;
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double v[3], x, y, z, xhd, yhd, zhd, f, xhdt, yhdt, zhdt,
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xaet, yaet, zaet, azobs, r, tz, w, del, cosdel,
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xaeo, yaeo, zaeo, zdobs, hmobs, dcobs, raobs;
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/* CIRS RA,Dec to Cartesian -HA,Dec. */
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iauS2c(ri-astrom->eral, di, v);
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x = v[0];
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y = v[1];
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z = v[2];
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/* Polar motion. */
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xhd = x + astrom->xpl*z;
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yhd = y - astrom->ypl*z;
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zhd = z - astrom->xpl*x + astrom->ypl*y;
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/* Diurnal aberration. */
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f = ( 1.0 - astrom->diurab*yhd );
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xhdt = f * xhd;
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yhdt = f * ( yhd + astrom->diurab );
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zhdt = f * zhd;
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/* Cartesian -HA,Dec to Cartesian Az,El (S=0,E=90). */
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xaet = astrom->sphi*xhdt - astrom->cphi*zhdt;
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yaet = yhdt;
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zaet = astrom->cphi*xhdt + astrom->sphi*zhdt;
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/* Azimuth (N=0,E=90). */
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azobs = ( xaet != 0.0 || yaet != 0.0 ) ? atan2(yaet,-xaet) : 0.0;
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/* ---------- */
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/* Refraction */
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/* ---------- */
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/* Cosine and sine of altitude, with precautions. */
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r = sqrt(xaet*xaet + yaet*yaet);
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r = r > CELMIN ? r : CELMIN;
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z = zaet > SELMIN ? zaet : SELMIN;
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/* A*tan(z)+B*tan^3(z) model, with Newton-Raphson correction. */
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tz = r/z;
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w = astrom->refb*tz*tz;
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del = ( astrom->refa + w ) * tz /
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( 1.0 + ( astrom->refa + 3.0*w ) / ( z*z ) );
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/* Apply the change, giving observed vector. */
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cosdel = 1.0 - del*del/2.0;
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f = cosdel - del*z/r;
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xaeo = xaet*f;
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yaeo = yaet*f;
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zaeo = cosdel*zaet + del*r;
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/* Observed ZD. */
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zdobs = atan2(sqrt(xaeo*xaeo+yaeo*yaeo), zaeo);
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/* Az/El vector to HA,Dec vector (both right-handed). */
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v[0] = astrom->sphi*xaeo + astrom->cphi*zaeo;
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v[1] = yaeo;
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v[2] = - astrom->cphi*xaeo + astrom->sphi*zaeo;
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/* To spherical -HA,Dec. */
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iauC2s ( v, &hmobs, &dcobs );
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/* Right ascension (with respect to CIO). */
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raobs = astrom->eral + hmobs;
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/* Return the results. */
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*aob = iauAnp(azobs);
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*zob = zdobs;
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*hob = -hmobs;
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*dob = dcobs;
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*rob = iauAnp(raobs);
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/* Finished. */
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/*----------------------------------------------------------------------
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**
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** Copyright (C) 2020
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** Standards Of Fundamental Astronomy Board
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** of the International Astronomical Union.
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**
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** =====================
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** SOFA Software License
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** =====================
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**
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** NOTICE TO USER:
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**
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** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
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** CONDITIONS WHICH APPLY TO ITS USE.
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**
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** 1. The Software is owned by the IAU SOFA Board ("SOFA").
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**
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** 2. Permission is granted to anyone to use the SOFA software for any
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** purpose, including commercial applications, free of charge and
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** without payment of royalties, subject to the conditions and
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** restrictions listed below.
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**
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** 3. You (the user) may copy and distribute SOFA source code to others,
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** and use and adapt its code and algorithms in your own software,
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** on a world-wide, royalty-free basis. That portion of your
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** distribution that does not consist of intact and unchanged copies
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** of SOFA source code files is a "derived work" that must comply
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** with the following requirements:
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**
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** a) Your work shall be marked or carry a statement that it
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** (i) uses routines and computations derived by you from
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** software provided by SOFA under license to you; and
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** (ii) does not itself constitute software provided by and/or
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** endorsed by SOFA.
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**
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** b) The source code of your derived work must contain descriptions
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** of how the derived work is based upon, contains and/or differs
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** from the original SOFA software.
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**
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** c) The names of all routines in your derived work shall not
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** include the prefix "iau" or "sofa" or trivial modifications
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** thereof such as changes of case.
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**
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** d) The origin of the SOFA components of your derived work must
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** not be misrepresented; you must not claim that you wrote the
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** original software, nor file a patent application for SOFA
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** software or algorithms embedded in the SOFA software.
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**
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** e) These requirements must be reproduced intact in any source
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** distribution and shall apply to anyone to whom you have
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** granted a further right to modify the source code of your
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** derived work.
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**
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** Note that, as originally distributed, the SOFA software is
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** intended to be a definitive implementation of the IAU standards,
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** and consequently third-party modifications are discouraged. All
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** variations, no matter how minor, must be explicitly marked as
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** such, as explained above.
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**
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** 4. You shall not cause the SOFA software to be brought into
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** disrepute, either by misuse, or use for inappropriate tasks, or
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** by inappropriate modification.
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**
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** 5. The SOFA software is provided "as is" and SOFA makes no warranty
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** as to its use or performance. SOFA does not and cannot warrant
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** the performance or results which the user may obtain by using the
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** SOFA software. SOFA makes no warranties, express or implied, as
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** to non-infringement of third party rights, merchantability, or
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** fitness for any particular purpose. In no event will SOFA be
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** liable to the user for any consequential, incidental, or special
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** damages, including any lost profits or lost savings, even if a
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** SOFA representative has been advised of such damages, or for any
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** claim by any third party.
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**
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** 6. The provision of any version of the SOFA software under the terms
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** and conditions specified herein does not imply that future
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** versions will also be made available under the same terms and
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** conditions.
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*
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** In any published work or commercial product which uses the SOFA
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** software directly, acknowledgement (see www.iausofa.org) is
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** appreciated.
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**
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** Correspondence concerning SOFA software should be addressed as
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** follows:
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**
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** By email: sofa@ukho.gov.uk
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** By post: IAU SOFA Center
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** HM Nautical Almanac Office
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** UK Hydrographic Office
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** Admiralty Way, Taunton
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** Somerset, TA1 2DN
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** United Kingdom
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**
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**--------------------------------------------------------------------*/
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}
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