Procedure

     CHGIRF ( Change inertial reference frames )

     SUBROUTINE CHGIRF ( REFA, REFB, ROTAB, NAME, INDEX )

Abstract

     Support changes among a standard set of inertial coordinate
     reference frames.

Required_Reading

     FRAMES

Keywords

     CONVERSION
     COORDINATES
     EPHEMERIS
     FRAMES
     MATRIX
     ROTATION
     TRANSFORMATION
     VECTOR

Declarations

     IMPLICIT NONE

     INCLUDE              'ninert.inc'
     INTEGER               REFA
     INTEGER               REFB
     DOUBLE PRECISION      ROTAB    ( 3,3 )
     CHARACTER*(*)         NAME
     INTEGER               INDEX

Brief_I/O

     VARIABLE  I/O  ENTRY POINTS
     --------  ---  --------------------------------------------------
     REFA       I   IRFROT
     REFB       I   IRFROT
     ROTAB      O   IRFROT
     NAME      I-O  IRFNUM, IRFNAM, IRFDEF
     INDEX     I-O  IRFNUM, IRFNAM

Detailed_Input

     See entry points IRFROT, IRFNUM, IRFNAM, and IRFDEF.

Detailed_Output

     See entry points IRFROT, IRFNUM, and IRFNAM.

Parameters

     None.

Exceptions

     1)  If CHGIRF is called directly, the signal, the error
         SPICE(BOGUSENTRY) is signaled.

     2)  See entry points IRFROT, IRFNUM, IRFNAM, and IRFDEF for
         exceptions specific to those routines.

Files

     None.

Particulars

     CHGIRF exists only as an umbrella for data to be shared
     by its entry points (IRFROT, IRFNUM, IRFNAM, and IRFDEF).
     It should never be called directly.

Examples

     See entry points IRFROT, IRFNUM, IRFNAM, and IRFDEF.

Restrictions

     None.

Literature_References

     [1]  J. Lieske, "Precession Matrix Based on IAU (1976) System of
          Astronomical Constants," Astron. Astrophys. 73, 282-284,
          1979.

     [2]  E. M. Standish, Jr., "Orientation of the JPL Ephemerides,
          DE 200/LE 200, to the Dynamical Equinox of J2000," Astron.
          Astrophys. 114, 297-302, 1982.

     [3]  E. M. Standish, Jr., "Conversion of Ephemeris Coordinates
          from the B1950 System to the J2000 System," JPL IOM
          314.6-581, 24 June 1985.

     [4]  E. M. Standish, Jr., "The Equinox Offsets of the JPL
          Ephemeris," JPL IOM 314.6-929, 26 February 1988.

     [5]  J. Lieske, "Expressions for the Precession Quantities Based
          upon the IAU (1976) System of Astronomical Constants,"
          Astron. Astrophys. 58, 1-16, 1977.

     [6]  L. Bass and R. Cesarone, "Mars Observer Planetary Constants
          and Models," JPL D-3444, November 1990.

     [7]  P. Kenneth Seidelmann (Ed.), "Explanatory Supplement to the
          Astronomical Almanac," University Science Books, 1992.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 4.5.0, 06-NOV-2021 (JDR) (NJB)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

        Corrected sign error in comments describing the angles used to
        convert between the J2000 and B1950 reference frames. Also
        corrected a typo in the comments.

    SPICELIB Version 4.4.0, 24-SEP-2013 (BVS)

        Updated entry point IRFNUM to treat J2000 as a special case
        and to not participate of CHKIN/CHOUT to increase efficiency.

    SPICELIB Version 4.3.0, 25-AUG-2005 (NJB)

        Updated to remove non-standard use of duplicate arguments
        in CONVRT, ROTMAT and MXM calls.

    SPICELIB Version 4.2.1, 04-JAN-2002 (EDW)

        Added DE-143 to header description for IRFROT.

    SPICELIB Version 4.2.0, 10-APR-1997 (WLT)

        A descriptive diagnostic was added to the entry points
        IRFROT and IRFDEF. Before they simply signaled the error
        with no diagnostic.

    SPICELIB Version 4.1.0, 14-OCT-1996 (WLT)

        The number of inertial frames recognized is now stored
        in the include file ninert.inc.

    SPICELIB Version 4.0.0, 20-MAY-1996 (WLT)

        The inertial frame DE-143 was added to the list of recognized
        inertial frames.

    SPICELIB Version 3.0.0, 20-MAR-1995 (WLT)

        The inertial frames DE-140 and DE-142  were added to the
        list of recognized inertial frames.

    SPICELIB Version 2.0.0, 30-JUL-1993 (WLT)

        The transformation from J2000 to B1950 was upgraded
        so that the transformation matrix produced matches
        the matrix given in [1].

        The frame MARSIAU was added to the list
        of recognized frames. This is the standard mars
        referenced inertial frame used by the Mars Observer
        project.

        Values for the obliquity of the ecliptic were taken
        from the Explanatory Supplement [7] to the Astronomical
        Almanac (1992) at both the epochs J2000 and B1950 and
        used to define the mean ecliptic and equinox frames
        ECLIPJ2000 and ECLIPB1950.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) (IMU)