apio¶
- erfa.apio(sp, theta, elong, phi, hm, xp, yp, refa, refb)[source]¶
For a terrestrial observer, prepare star-independent astrometry parameters for transformations between CIRS and observed coordinates.
- Parameters:
- spdouble array
- thetadouble array
- elongdouble array
- phidouble array
- hmdouble array
- xpdouble array
- ypdouble array
- refadouble array
- refbdouble array
- Returns:
- astromeraASTROM array
Notes
Wraps ERFA function
eraApio
. The ERFA documentation is:- - - - - - - - e r a A p i o - - - - - - - - For a terrestrial observer, prepare star-independent astrometry parameters for transformations between CIRS and observed coordinates. The caller supplies the Earth orientation information and the refraction constants as well as the site coordinates. Given: sp double the TIO locator s' (radians, Note 1) theta double Earth rotation angle (radians) elong double longitude (radians, east +ve, Note 2) phi double geodetic latitude (radians, Note 2) hm double height above ellipsoid (m, geodetic Note 2) xp,yp double polar motion coordinates (radians, Note 3) refa double refraction constant A (radians, Note 4) refb double refraction constant B (radians, Note 4) Returned: astrom eraASTROM star-independent astrometry parameters: pmt double unchanged eb double[3] unchanged eh double[3] unchanged em double unchanged v double[3] unchanged bm1 double unchanged bpn double[3][3] unchanged along double adjusted longitude (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) Notes: 1) sp, the TIO locator s', is a tiny quantity needed only by the most precise applications. It can either be set to zero or predicted using the ERFA function eraSp00. 2) The geographical coordinates are with respect to the ERFA_WGS84 reference ellipsoid. TAKE CARE WITH THE LONGITUDE SIGN: the longitude required by the present function is east-positive (i.e. right-handed), in accordance with geographical convention. 3) The polar motion xp,yp can be obtained from IERS bulletins. The values are the coordinates (in radians) of the Celestial Intermediate Pole with respect to the International Terrestrial Reference System (see IERS Conventions 2003), measured along the meridians 0 and 90 deg west respectively. For many applications, xp and yp can be set to zero. Internally, the polar motion is stored in a form rotated onto the local meridian. 4) The refraction constants refa and refb are for use in a dZ = A*tan(Z)+B*tan^3(Z) model, where Z is the observed (i.e. refracted) zenith distance and dZ is the amount of refraction. 5) 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. 6) In cases where the caller does not wish to provide the Earth rotation information and refraction constants, the function eraApio13 can be used instead of the present function. This starts from UTC and weather readings etc. and computes suitable values using other ERFA functions. 7) This is one of several functions that inserts into the astrom structure star-independent parameters needed for the chain of astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed. The various functions support different classes of observer and portions of the transformation chain: functions observer transformation eraApcg eraApcg13 geocentric ICRS <-> GCRS eraApci eraApci13 terrestrial ICRS <-> CIRS eraApco eraApco13 terrestrial ICRS <-> observed eraApcs eraApcs13 space ICRS <-> GCRS eraAper eraAper13 terrestrial update Earth rotation eraApio eraApio13 terrestrial CIRS <-> observed Those with names ending in "13" use contemporary ERFA models to compute the various ephemerides. The others accept ephemerides supplied by the caller. The transformation from ICRS to GCRS covers space motion, parallax, light deflection, and aberration. From GCRS to CIRS comprises frame bias and precession-nutation. From CIRS to observed takes account of Earth rotation, polar motion, diurnal aberration and parallax (unless subsumed into the ICRS <-> GCRS transformation), and atmospheric refraction. 8) The context structure astrom produced by this function is used by eraAtioq and eraAtoiq. Called: eraIr initialize r-matrix to identity eraRz rotate around Z-axis eraRy rotate around Y-axis eraRx rotate around X-axis eraAnpm normalize angle into range +/- pi eraPvtob position/velocity of terrestrial station This revision: 2021 February 24 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.