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eraBp00

[rb, rp, rbp] = ERFA.bp00(date1, date2)

Frame bias and precession, IAU 2000.

Given:

   date1,date2  double         TT as a 2-part Julian Date (Note 1)

Returned:

   rb           double[3][3]   frame bias matrix (Note 2)
   rp           double[3][3]   precession matrix (Note 3)
   rbp          double[3][3]   bias-precession matrix (Note 4)

Notes:

  1. The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others:
           date1         date2

       2450123.7           0.0       (JD method)
       2451545.0       -1421.3       (J2000 method)
       2400000.5       50123.2       (MJD method)
       2450123.5           0.2       (date & time method)

The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience.

  1. The matrix rb transforms vectors from GCRS to mean J2000.0 by applying frame bias.

  2. The matrix rp transforms vectors from J2000.0 mean equator and equinox to mean equator and equinox of date by applying precession.

  3. The matrix rbp transforms vectors from GCRS to mean equator and equinox of date by applying frame bias then precession. It is the product rp x rb.

  4. It is permissible to re-use the same array in the returned arguments. The arrays are filled in the order given.

Called:

   eraBi00      frame bias components, IAU 2000
   eraPr00      IAU 2000 precession adjustments
   eraIr        initialize r-matrix to identity
   eraRx        rotate around X-axis
   eraRy        rotate around Y-axis
   eraRz        rotate around Z-axis
   eraCr        copy r-matrix
   eraRxr       product of two r-matrices

Reference:

"Expressions for the Celestial Intermediate Pole and Celestial Ephemeris Origin consistent with the IAU 2000A precession- nutation model", Astron.Astrophys. 400, 1145-1154 (2003)

n.b. The celestial ephemeris origin (CEO) was renamed "celestial intermediate origin" (CIO) by IAU 2006 Resolution 2.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.