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use IauAstrom;
/// Insert ERA into context
///
/// In the star-independent astrometry parameters, update only the
/// Earth rotation angle, supplied by the caller explicitly.
///
/// This function is part of the International Astronomical Union's
/// SOFA (Standards of Fundamental Astronomy) software collection.
///
/// Status: support function.
///
/// Given:
/// ```
/// theta double Earth rotation angle (radians, Note 2)
/// astrom iauASTROM* 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 iauASTROM* 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 iauAper13 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
///
/// iauApcg iauApcg13 geocentric ICRS <-> GCRS
/// iauApci iauApci13 terrestrial ICRS <-> CIRS
/// iauApco iauApco13 terrestrial ICRS <-> observed
/// iauApcs iauApcs13 space ICRS <-> GCRS
/// iauAper iauAper13 terrestrial update Earth rotation
/// iauApio iauApio13 terrestrial CIRS <-> observed
/// ```
/// Those with names ending in "13" use contemporary SOFA 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.