aper¶
- erfa.aper(theta, astrom)[source]¶
In the star-independent astrometry parameters, update only the Earth rotation angle, supplied by the caller explicitly.
- Parameters:
- thetadouble array
- astromeraASTROM array
- Returns:
- astromeraASTROM array
Notes
Wraps ERFA function
eraAper
. Note that, unlike the erfa routine, the python wrapper does not change astrom in-place. The ERFA documentation is:- - - - - - - - e r a A p e r - - - - - - - - In the star-independent astrometry parameters, update only the Earth rotation angle, supplied by the caller explicitly. Given: theta double Earth rotation angle (radians, Note 2) astrom eraASTROM star-independent astrometry parameters: pmt double not used eb double[3] not used eh double[3] not used em double not used v double[3] not used bm1 double not used bpn double[3][3] not used along double longitude + s' (radians) xpl double not used ypl double not used sphi double not used cphi double not used diurab double not used eral double not used refa double not used refb double not used 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 unchanged xpl double unchanged ypl double unchanged sphi double unchanged cphi double unchanged diurab double unchanged eral double "local" Earth rotation angle (radians) refa double unchanged refb double unchanged Notes: 1) This function exists to enable sidereal-tracking applications to avoid wasteful recomputation of the bulk of the astrometry parameters: only the Earth rotation is updated. 2) For targets expressed as equinox based positions, such as classical geocentric apparent (RA,Dec), the supplied theta can be Greenwich apparent sidereal time rather than Earth rotation angle. 3) The function eraAper13 can be used instead of the present function, and starts from UT1 rather than ERA itself. 4) 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. This revision: 2013 September 25 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.