[rc, dc] = ERFA.aticqn(ri, di, astrom, n, b)Quick CIRS to ICRS astrometric place transformation, given the star- independent astrometry parameters plus a list of light-deflecting bodies.
Use of this function is appropriate when efficiency is important and where many star positions are all to be transformed for one date. The star-independent astrometry parameters can be obtained by calling one of the functions eraApci, eraApcg, eraApco or eraApcs. *
- If the only light-deflecting body to be taken into account is the
- Sun, the eraAticq function can be used instead.
ri,di double CIRS RA,Dec (radians)
astrom ASTROM* star-independent astrometry parameters:
pmt double PM time interval (SSB, Julian years)
eb double[3] SSB to observer (vector, au)
eh double[3] Sun to observer (unit vector)
em double distance from Sun to observer (au)
v double[3] barycentric observer velocity (vector, c)
bm1 double sqrt(1-|v|^2): reciprocal of Lorenz factor
bpn double[3][3] bias-precession-nutation matrix
along double longitude + s' (radians)
xpl double polar motion xp wrt local meridian (radians)
ypl double polar motion yp wrt local meridian (radians)
sphi double sine of geodetic latitude
cphi double cosine of geodetic latitude
diurab double magnitude of diurnal aberration vector
eral double "local" Earth rotation angle (radians)
refa double refraction constant A (radians)
refb double refraction constant B (radians)
n int number of bodies (Note 3)
b LDBODY[n] data for each of the n bodies (Notes 3,4):
bm double mass of the body (solar masses, Note 5)
dl double deflection limiter (Note 6)
pv [2][3] barycentric PV of the body (au, au/day)
rc,dc double ICRS astrometric RA,Dec (radians)
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Iterative techniques are used for the aberration and light deflection corrections so that the functions eraAticqn and eraAtciqn are accurate inverses; even at the edge of the Sun's disk the discrepancy is only about 1 nanoarcsecond.
-
If the only light-deflecting body to be taken into account is the Sun, the eraAticq function can be used instead.
-
The struct b contains n entries, one for each body to be considered. If n = 0, no gravitational light deflection will be applied, not even for the Sun.
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The struct b should include an entry for the Sun as well as for any planet or other body to be taken into account. The entries should be in the order in which the light passes the body.
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In the entry in the b struct for body i, the mass parameter b[i].bm can, as required, be adjusted in order to allow for such effects as quadrupole field.
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The deflection limiter parameter b[i].dl is phi^2/2, where phi is the angular separation (in radians) between star and body at which limiting is applied. As phi shrinks below the chosen threshold, the deflection is artificially reduced, reaching zero for phi = 0. Example values suitable for a terrestrial observer, together with masses, are as follows:
body i b[i].bm b[i].dl
Sun 1.0 6e-6
Jupiter 0.00095435 3e-9
Saturn 0.00028574 3e-10
- For efficiency, validation of the contents of the b array is omitted. The supplied masses must be greater than zero, the position and velocity vectors must be right, and the deflection limiter greater than zero.
eraS2c spherical coordinates to unit vector
eraTrxp product of transpose of r-matrix and p-vector
eraZp zero p-vector
eraAb stellar aberration
eraLdn light deflection by n bodies
eraC2s p-vector to spherical
eraAnp normalize angle into range +/- pi
This revision: 2021 January 6
Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.