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Diffstat (limited to 'ast/erfa/starpm.c')
| -rw-r--r-- | ast/erfa/starpm.c | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/ast/erfa/starpm.c b/ast/erfa/starpm.c new file mode 100644 index 0000000..69b7708 --- /dev/null +++ b/ast/erfa/starpm.c @@ -0,0 +1,214 @@ +#include "erfa.h" + +int eraStarpm(double ra1, double dec1, + double pmr1, double pmd1, double px1, double rv1, + double ep1a, double ep1b, double ep2a, double ep2b, + double *ra2, double *dec2, + double *pmr2, double *pmd2, double *px2, double *rv2) +/* +** - - - - - - - - - - +** e r a S t a r p m +** - - - - - - - - - - +** +** Star proper motion: update star catalog data for space motion. +** +** Given: +** ra1 double right ascension (radians), before +** dec1 double declination (radians), before +** pmr1 double RA proper motion (radians/year), before +** pmd1 double Dec proper motion (radians/year), before +** px1 double parallax (arcseconds), before +** rv1 double radial velocity (km/s, +ve = receding), before +** ep1a double "before" epoch, part A (Note 1) +** ep1b double "before" epoch, part B (Note 1) +** ep2a double "after" epoch, part A (Note 1) +** ep2b double "after" epoch, part B (Note 1) +** +** Returned: +** ra2 double right ascension (radians), after +** dec2 double declination (radians), after +** pmr2 double RA proper motion (radians/year), after +** pmd2 double Dec proper motion (radians/year), after +** px2 double parallax (arcseconds), after +** rv2 double radial velocity (km/s, +ve = receding), after +** +** Returned (function value): +** int status: +** -1 = system error (should not occur) +** 0 = no warnings or errors +** 1 = distance overridden (Note 6) +** 2 = excessive velocity (Note 7) +** 4 = solution didn't converge (Note 8) +** else = binary logical OR of the above warnings +** +** Notes: +** +** 1) The starting and ending TDB dates ep1a+ep1b and ep2a+ep2b are +** Julian Dates, apportioned in any convenient way between the two +** parts (A and B). For example, JD(TDB)=2450123.7 could be +** expressed in any of these ways, among others: +** +** epna epnb +** +** 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. +** +** 2) 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. +** +** The proper motions are the rate of change of the right ascension +** and declination at the catalog epoch and are in radians per TDB +** Julian year. +** +** The parallax and radial velocity are in the same frame. +** +** 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. +** +** 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 eraStarpv +** function for the value used). 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 in the function eraStarpv), it is arbitrarily set +** to zero. When this action occurs, 2 is added to the status. +** +** 8) The relativistic adjustment carried out in the eraStarpv function +** involves an iterative calculation. If the process fails to +** converge within a set number of iterations, 4 is added to the +** status. +** +** Called: +** eraStarpv star catalog data to space motion pv-vector +** eraPvu update a pv-vector +** eraPdp scalar product of two p-vectors +** eraPvstar space motion pv-vector to star catalog data +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double pv1[2][3], tl1, dt, pv[2][3], r2, rdv, v2, c2mv2, tl2, + pv2[2][3]; + int j1, j2, j; + + +/* RA,Dec etc. at the "before" epoch to space motion pv-vector. */ + j1 = eraStarpv(ra1, dec1, pmr1, pmd1, px1, rv1, pv1); + +/* Light time when observed (days). */ + tl1 = eraPm(pv1[0]) / ERFA_DC; + +/* Time interval, "before" to "after" (days). */ + dt = (ep2a - ep1a) + (ep2b - ep1b); + +/* Move star along track from the "before" observed position to the */ +/* "after" geometric position. */ + eraPvu(dt + tl1, pv1, pv); + +/* From this geometric position, deduce the observed light time (days) */ +/* at the "after" epoch (with theoretically unneccessary error check). */ + r2 = eraPdp(pv[0], pv[0]); + rdv = eraPdp(pv[0], pv[1]); + v2 = eraPdp(pv[1], pv[1]); + c2mv2 = ERFA_DC*ERFA_DC - v2; + if (c2mv2 <= 0) return -1; + tl2 = (-rdv + sqrt(rdv*rdv + c2mv2*r2)) / c2mv2; + +/* Move the position along track from the observed place at the */ +/* "before" epoch to the observed place at the "after" epoch. */ + eraPvu(dt + (tl1 - tl2), pv1, pv2); + +/* Space motion pv-vector to RA,Dec etc. at the "after" epoch. */ + j2 = eraPvstar(pv2, ra2, dec2, pmr2, pmd2, px2, rv2); + +/* Final status. */ + j = (j2 == 0) ? j1 : -1; + + return j; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |