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authorWilliam Joye <wjoye@cfa.harvard.edu>2017-12-08 18:57:06 (GMT)
committerWilliam Joye <wjoye@cfa.harvard.edu>2017-12-08 18:57:06 (GMT)
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-#include "erfa.h"
-
-int eraStarpv(double ra, double dec,
- double pmr, double pmd, double px, double rv,
- double pv[2][3])
-/*
-** - - - - - - - - - -
-** e r a S t a r p v
-** - - - - - - - - - -
-**
-** Convert star catalog coordinates to position+velocity vector.
-**
-** Given (Note 1):
-** ra double right ascension (radians)
-** dec double declination (radians)
-** pmr double RA proper motion (radians/year)
-** pmd double Dec proper motion (radians/year)
-** px double parallax (arcseconds)
-** rv double radial velocity (km/s, positive = receding)
-**
-** Returned (Note 2):
-** pv double[2][3] pv-vector (AU, AU/day)
-**
-** Returned (function value):
-** int status:
-** 0 = no warnings
-** 1 = distance overridden (Note 6)
-** 2 = excessive speed (Note 7)
-** 4 = solution didn't converge (Note 8)
-** else = binary logical OR of the above
-**
-** Notes:
-**
-** 1) The star data accepted by this function are "observables" for an
-** imaginary observer at the solar-system barycenter. Proper motion
-** and radial velocity are, strictly, in terms of barycentric
-** coordinate time, TCB. For most practical applications, it is
-** permissible to neglect the distinction between TCB and ordinary
-** "proper" time on Earth (TT/TAI). The result will, as a rule, be
-** limited by the intrinsic accuracy of the proper-motion and
-** radial-velocity data; moreover, the pv-vector is likely to be
-** merely an intermediate result, so that a change of time unit
-** would cancel out overall.
-**
-** In accordance with normal star-catalog conventions, the object's
-** right ascension and declination are freed from the effects of
-** secular aberration. The frame, which is aligned to the catalog
-** equator and equinox, is Lorentzian and centered on the SSB.
-**
-** 2) The resulting position and velocity pv-vector is with respect to
-** the same frame and, like the catalog coordinates, is freed from
-** the effects of secular aberration. Should the "coordinate
-** direction", where the object was located at the catalog epoch, be
-** required, it may be obtained by calculating the magnitude of the
-** position vector pv[0][0-2] dividing by the speed of light in
-** AU/day to give the light-time, and then multiplying the space
-** velocity pv[1][0-2] by this light-time and adding the result to
-** pv[0][0-2].
-**
-** Summarizing, the pv-vector returned is for most stars almost
-** identical to the result of applying the standard geometrical
-** "space motion" transformation. The differences, which are the
-** subject of the Stumpff paper referenced below, are:
-**
-** (i) In stars with significant radial velocity and proper motion,
-** the constantly changing light-time distorts the apparent proper
-** motion. Note that this is a classical, not a relativistic,
-** effect.
-**
-** (ii) The transformation complies with special relativity.
-**
-** 3) Care is needed with units. The star coordinates are in radians
-** and the proper motions in radians per Julian year, but the
-** parallax is in arcseconds; the radial velocity is in km/s, but
-** the pv-vector result is in AU and AU/day.
-**
-** 4) The RA proper motion is in terms of coordinate angle, not true
-** angle. If the catalog uses arcseconds for both RA and Dec proper
-** motions, the RA proper motion will need to be divided by cos(Dec)
-** before use.
-**
-** 5) Straight-line motion at constant speed, in the inertial frame,
-** is assumed.
-**
-** 6) An extremely small (or zero or negative) parallax is interpreted
-** to mean that the object is on the "celestial sphere", the radius
-** of which is an arbitrary (large) value (see the constant PXMIN).
-** When the distance is overridden in this way, the status,
-** initially zero, has 1 added to it.
-**
-** 7) If the space velocity is a significant fraction of c (see the
-** constant VMAX), it is arbitrarily set to zero. When this action
-** occurs, 2 is added to the status.
-**
-** 8) The relativistic adjustment involves an iterative calculation.
-** If the process fails to converge within a set number (IMAX) of
-** iterations, 4 is added to the status.
-**
-** 9) The inverse transformation is performed by the function
-** eraPvstar.
-**
-** Called:
-** eraS2pv spherical coordinates to pv-vector
-** eraPm modulus of p-vector
-** eraZp zero p-vector
-** eraPn decompose p-vector into modulus and direction
-** eraPdp scalar product of two p-vectors
-** eraSxp multiply p-vector by scalar
-** eraPmp p-vector minus p-vector
-** eraPpp p-vector plus p-vector
-**
-** Reference:
-**
-** Stumpff, P., 1985, Astron.Astrophys. 144, 232-240.
-**
-** Copyright (C) 2013-2016, NumFOCUS Foundation.
-** Derived, with permission, from the SOFA library. See notes at end of file.
-*/
-{
-/* Smallest allowed parallax */
- static const double PXMIN = 1e-7;
-
-/* Largest allowed speed (fraction of c) */
- static const double VMAX = 0.5;
-
-/* Maximum number of iterations for relativistic solution */
- static const int IMAX = 100;
-
- int i, iwarn;
- double w, r, rd, rad, decd, v, x[3], usr[3], ust[3],
- vsr, vst, betst, betsr, bett, betr,
- dd, ddel, ur[3], ut[3],
- d = 0.0, del = 0.0, /* to prevent */
- odd = 0.0, oddel = 0.0, /* compiler */
- od = 0.0, odel = 0.0; /* warnings */
-
-
-/* Distance (AU). */
- if (px >= PXMIN) {
- w = px;
- iwarn = 0;
- } else {
- w = PXMIN;
- iwarn = 1;
- }
- r = ERFA_DR2AS / w;
-
-/* Radial velocity (AU/day). */
- rd = ERFA_DAYSEC * rv * 1e3 / ERFA_DAU;
-
-/* Proper motion (radian/day). */
- rad = pmr / ERFA_DJY;
- decd = pmd / ERFA_DJY;
-
-/* To pv-vector (AU,AU/day). */
- eraS2pv(ra, dec, r, rad, decd, rd, pv);
-
-/* If excessive velocity, arbitrarily set it to zero. */
- v = eraPm(pv[1]);
- if (v / ERFA_DC > VMAX) {
- eraZp(pv[1]);
- iwarn += 2;
- }
-
-/* Isolate the radial component of the velocity (AU/day). */
- eraPn(pv[0], &w, x);
- vsr = eraPdp(x, pv[1]);
- eraSxp(vsr, x, usr);
-
-/* Isolate the transverse component of the velocity (AU/day). */
- eraPmp(pv[1], usr, ust);
- vst = eraPm(ust);
-
-/* Special-relativity dimensionless parameters. */
- betsr = vsr / ERFA_DC;
- betst = vst / ERFA_DC;
-
-/* Determine the inertial-to-observed relativistic correction terms. */
- bett = betst;
- betr = betsr;
- for (i = 0; i < IMAX; i++) {
- d = 1.0 + betr;
- del = sqrt(1.0 - betr*betr - bett*bett) - 1.0;
- betr = d * betsr + del;
- bett = d * betst;
- if (i > 0) {
- dd = fabs(d - od);
- ddel = fabs(del - odel);
- if ((i > 1) && (dd >= odd) && (ddel >= oddel)) break;
- odd = dd;
- oddel = ddel;
- }
- od = d;
- odel = del;
- }
- if (i >= IMAX) iwarn += 4;
-
-/* Replace observed radial velocity with inertial value. */
- w = (betsr != 0.0) ? d + del / betsr : 1.0;
- eraSxp(w, usr, ur);
-
-/* Replace observed tangential velocity with inertial value. */
- eraSxp(d, ust, ut);
-
-/* Combine the two to obtain the inertial space velocity. */
- eraPpp(ur, ut, pv[1]);
-
-/* Return the status. */
- return iwarn;
-
-}
-/*----------------------------------------------------------------------
-**
-**
-** 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.
-**
-*/