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Diffstat (limited to 'ast/erfa/pmsafe.c')
| -rw-r--r-- | ast/erfa/pmsafe.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/ast/erfa/pmsafe.c b/ast/erfa/pmsafe.c new file mode 100644 index 0000000..02e5824 --- /dev/null +++ b/ast/erfa/pmsafe.c @@ -0,0 +1,206 @@ +#include "erfa.h" + +int eraPmsafe(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 P m s a f e +** - - - - - - - - - - +** +** Star proper motion: update star catalog data for space motion, with +** special handling to handle the zero parallax case. +** +** 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 epochs 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 overridden +** to ensure that the object is at a finite but very large distance, +** but not so large that the proper motion is equivalent to a large +** but safe speed (about 0.1c using the chosen constant). A warning +** status of 1 is added to the status if this action has been taken. +** +** 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: +** eraSeps angle between two points +** eraStarpm update star catalog data for space motion +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + +/* Minimum allowed parallax (arcsec) */ + const double PXMIN = 5e-7; + +/* Factor giving maximum allowed transverse speed of about 1% c */ + const double F = 326.0; + + int jpx, j; + double pm, px1a; + + +/* Proper motion in one year (radians). */ + pm = eraSeps(ra1, dec1, ra1+pmr1, dec1+pmd1); + +/* Override the parallax to reduce the chances of a warning status. */ + jpx = 0; + px1a = px1; + pm *= F; + if (px1a < pm) {jpx = 1; px1a = pm;} + if (px1a < PXMIN) {jpx = 1; px1a = PXMIN;} + +/* Carry out the transformation using the modified parallax. */ + j = eraStarpm(ra1, dec1, pmr1, pmd1, px1a, rv1, + ep1a, ep1b, ep2a, ep2b, + ra2, dec2, pmr2, pmd2, px2, rv2); + +/* Revise and return the status. */ + if ( !(j%2) ) j += jpx; + return j; + +/* Finished. */ + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |