ld¶
- erfa.ld(bm, p, q, e, em, dlim)[source]¶
Apply light deflection by a solar-system body, as part of transforming coordinate direction into natural direction.
- Parameters:
- bmdouble array
- pdouble array
- qdouble array
- edouble array
- emdouble array
- dlimdouble array
- Returns:
- p1double array
Notes
Wraps ERFA function
eraLd
. The ERFA documentation is:- - - - - - e r a L d - - - - - - Apply light deflection by a solar-system body, as part of transforming coordinate direction into natural direction. Given: bm double mass of the gravitating body (solar masses) p double[3] direction from observer to source (unit vector) q double[3] direction from body to source (unit vector) e double[3] direction from body to observer (unit vector) em double distance from body to observer (au) dlim double deflection limiter (Note 4) Returned: p1 double[3] observer to deflected source (unit vector) Notes: 1) The algorithm is based on Expr. (70) in Klioner (2003) and Expr. (7.63) in the Explanatory Supplement (Urban & Seidelmann 2013), with some rearrangement to minimize the effects of machine precision. 2) The mass parameter bm can, as required, be adjusted in order to allow for such effects as quadrupole field. 3) The barycentric position of the deflecting body should ideally correspond to the time of closest approach of the light ray to the body. 4) The deflection limiter parameter dlim is phi^2/2, where phi is the angular separation (in radians) between source and body at which limiting is applied. As phi shrinks below the chosen threshold, the deflection is artificially reduced, reaching zero for phi = 0. 5) The returned vector p1 is not normalized, but the consequential departure from unit magnitude is always negligible. 6) The arguments p and p1 can be the same array. 7) To accumulate total light deflection taking into account the contributions from several bodies, call the present function for each body in succession, in decreasing order of distance from the observer. 8) For efficiency, validation is omitted. The supplied vectors must be of unit magnitude, and the deflection limiter non-zero and positive. References: Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to the Astronomical Almanac, 3rd ed., University Science Books (2013). Klioner, Sergei A., "A practical relativistic model for micro- arcsecond astrometry in space", Astr. J. 125, 1580-1597 (2003). Called: eraPdp scalar product of two p-vectors eraPxp vector product of two p-vectors This revision: 2021 February 24 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.