atoiq¶
- erfa.atoiq(type, ob1, ob2, astrom)[source]¶
Quick observed place to CIRS, given the star-independent astrometry parameters.
- Parameters:
- typeconst char array
- ob1double array
- ob2double array
- astromeraASTROM array
- Returns:
- ridouble array
- didouble array
Notes
Wraps ERFA function
eraAtoiq. The ERFA documentation is:- - - - - - - - - e r a A t o i q - - - - - - - - - Quick observed place to CIRS, given the star-independent astrometry parameters. 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 eraApio[13] or eraApco[13]. Given: type char[] type of coordinates: "R", "H" or "A" (Note 1) ob1 double observed Az, HA or RA (radians; Az is N=0,E=90) ob2 double observed ZD or Dec (radians) astrom eraASTROM* 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) Returned: ri double CIRS right ascension (CIO-based, radians) di double CIRS declination (radians) Notes: 1) "Observed" Az,ZD means the position that would be seen by a perfect geodetically aligned theodolite. This is related to the observed HA,Dec via the standard rotation, using the geodetic latitude (corrected for polar motion), while the observed HA and (CIO-based) RA are related simply through the Earth rotation angle and the site longitude. "Observed" RA,Dec or HA,Dec thus means the position that would be seen by a perfect equatorial with its polar axis aligned to the Earth's axis of rotation. 2) Only the first character of the type argument is significant. "R" or "r" indicates that ob1 and ob2 are the observed right ascension (CIO-based) and declination; "H" or "h" indicates that they are hour angle (west +ve) and declination; anything else ("A" or "a" is recommended) indicates that ob1 and ob2 are azimuth (north zero, east 90 deg) and zenith distance. (Zenith distance is used rather than altitude in order to reflect the fact that no allowance is made for depression of the horizon.) 3) The accuracy of the result is limited by the corrections for refraction, which use a simple A*tan(z) + B*tan^3(z) model. Providing the meteorological parameters are known accurately and there are no gross local effects, the predicted intermediate coordinates should be within 0.05 arcsec (optical) or 1 arcsec (radio) for a zenith distance of less than 70 degrees, better than 30 arcsec (optical or radio) at 85 degrees and better than 20 arcmin (optical) or 25 arcmin (radio) at the horizon. Without refraction, the complementary functions eraAtioq and eraAtoiq are self-consistent to better than 1 microarcsecond all over the celestial sphere. With refraction included, consistency falls off at high zenith distances, but is still better than 0.05 arcsec at 85 degrees. 4) It is advisable to take great care with units, as even unlikely values of the input parameters are accepted and processed in accordance with the models used. Called: eraS2c spherical coordinates to unit vector eraC2s p-vector to spherical eraAnp normalize angle into range 0 to 2pi This revision: 2022 August 30 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.