pmsafe.c

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#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) 2013-2015, 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) 2013-2015, 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
**  
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**  modification, are permitted provided that the following conditions
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**  
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