summaryrefslogtreecommitdiffstats
path: root/ast/erfa/pvstar.c
diff options
context:
space:
mode:
authorWilliam Joye <wjoye@cfa.harvard.edu>2019-05-10 16:18:58 (GMT)
committerWilliam Joye <wjoye@cfa.harvard.edu>2019-05-10 16:18:58 (GMT)
commit5492ad5105428df25cca70ab260229f757427278 (patch)
treee2bc900ba8c297d483518d1e86405e2e0f86f0ea /ast/erfa/pvstar.c
parent9646e8d50bc1481de77459d59738826f9c256ad6 (diff)
downloadblt-5492ad5105428df25cca70ab260229f757427278.zip
blt-5492ad5105428df25cca70ab260229f757427278.tar.gz
blt-5492ad5105428df25cca70ab260229f757427278.tar.bz2
upgrade ast 8.7.1
Diffstat (limited to 'ast/erfa/pvstar.c')
-rw-r--r--ast/erfa/pvstar.c216
1 files changed, 216 insertions, 0 deletions
diff --git a/ast/erfa/pvstar.c b/ast/erfa/pvstar.c
new file mode 100644
index 0000000..3a4e00b
--- /dev/null
+++ b/ast/erfa/pvstar.c
@@ -0,0 +1,216 @@
+#include "erfa.h"
+
+int eraPvstar(double pv[2][3], double *ra, double *dec,
+ double *pmr, double *pmd, double *px, double *rv)
+/*
+** - - - - - - - - - -
+** e r a P v s t a r
+** - - - - - - - - - -
+**
+** Convert star position+velocity vector to catalog coordinates.
+**
+** Given (Note 1):
+** pv double[2][3] pv-vector (AU, AU/day)
+**
+** Returned (Note 2):
+** 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 (arcsec)
+** rv double radial velocity (km/s, positive = receding)
+**
+** Returned (function value):
+** int status:
+** 0 = OK
+** -1 = superluminal speed (Note 5)
+** -2 = null position vector
+**
+** Notes:
+**
+** 1) The specified pv-vector is the coordinate direction (and its rate
+** of change) for the date at which the light leaving the star
+** reached the solar-system barycenter.
+**
+** 2) The star data returned 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 supplied pv-vector is likely
+** to be merely an intermediate result (for example generated by the
+** function eraStarpv), so that a change of time unit will 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.
+**
+** Summarizing, the specified pv-vector is for most stars almost
+** identical to the result of applying the standard geometrical
+** "space motion" transformation to the catalog data. The
+** differences, which are the subject of the Stumpff paper cited
+** 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 proper motions are the rate of change of the right ascension
+** and declination at the catalog epoch and are in radians per Julian
+** year. The RA proper motion is in terms of coordinate angle, not
+** true angle, and will thus be numerically larger at high
+** declinations.
+**
+** 5) Straight-line motion at constant speed in the inertial frame is
+** assumed. If the speed is greater than or equal to the speed of
+** light, the function aborts with an error status.
+**
+** 6) The inverse transformation is performed by the function eraStarpv.
+**
+** Called:
+** 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
+** eraPm modulus of p-vector
+** eraPpp p-vector plus p-vector
+** eraPv2s pv-vector to spherical
+** eraAnp normalize angle into range 0 to 2pi
+**
+** 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.
+*/
+{
+ double r, x[3], vr, ur[3], vt, ut[3], bett, betr, d, w, del,
+ usr[3], ust[3], a, rad, decd, rd;
+
+
+/* Isolate the radial component of the velocity (AU/day, inertial). */
+ eraPn(pv[0], &r, x);
+ vr = eraPdp(x, pv[1]);
+ eraSxp(vr, x, ur);
+
+/* Isolate the transverse component of the velocity (AU/day, inertial). */
+ eraPmp(pv[1], ur, ut);
+ vt = eraPm(ut);
+
+/* Special-relativity dimensionless parameters. */
+ bett = vt / ERFA_DC;
+ betr = vr / ERFA_DC;
+
+/* The inertial-to-observed correction terms. */
+ d = 1.0 + betr;
+ w = 1.0 - betr*betr - bett*bett;
+ if (d == 0.0 || w < 0) return -1;
+ del = sqrt(w) - 1.0;
+
+/* Apply relativistic correction factor to radial velocity component. */
+ w = (betr != 0) ? (betr - del) / (betr * d) : 1.0;
+ eraSxp(w, ur, usr);
+
+/* Apply relativistic correction factor to tangential velocity */
+/* component. */
+ eraSxp(1.0/d, ut, ust);
+
+/* Combine the two to obtain the observed velocity vector (AU/day). */
+ eraPpp(usr, ust, pv[1]);
+
+/* Cartesian to spherical. */
+ eraPv2s(pv, &a, dec, &r, &rad, &decd, &rd);
+ if (r == 0.0) return -2;
+
+/* Return RA in range 0 to 2pi. */
+ *ra = eraAnp(a);
+
+/* Return proper motions in radians per year. */
+ *pmr = rad * ERFA_DJY;
+ *pmd = decd * ERFA_DJY;
+
+/* Return parallax in arcsec. */
+ *px = ERFA_DR2AS / r;
+
+/* Return radial velocity in km/s. */
+ *rv = 1e-3 * rd * ERFA_DAU / ERFA_DAYSEC;
+
+/* OK status. */
+ return 0;
+
+}
+/*----------------------------------------------------------------------
+**
+**
+** 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.
+**
+*/