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Procedure
Abstract
Required_Reading
Keywords
Declarations
Brief_I/O
Detailed_Input
Detailed_Output
Parameters
Exceptions
Files
Particulars
Examples
Restrictions
Literature_References
Author_and_Institution
Version

Procedure

 IRFNUM ( Inertial reference frame number )
 
      ENTRY IRFNUM ( NAME, INDEX )
 

Abstract

     Return the index of one of the standard inertial reference
     frames supported by IRFROT.

Required_Reading

     FRAMES

Keywords

     CONVERSION
     COORDINATES
     EPHEMERIS
     FRAMES
     MATRIX
     ROTATION
     TRANSFORMATION
     VECTOR

Declarations

     CHARACTER*(*)         NAME
     INTEGER               INDEX

Brief_I/O

     Variable  I/O  Description
     --------  ---  --------------------------------------------------
     NAME       I   Name of standard inertial reference frame.
     INDEX      O   Index of frame.

Detailed_Input

     NAME        is the name of one of the standard inertial
                 reference frames supported by IRFROT, or
                 'DEFAULT'.

Detailed_Output

     INDEX       is the index of the frame specified by NAME.

Parameters

      None.

Exceptions

     1) If NAME is not recognized, INDEX is zero.

     2) If no default frame has been specified, INDEX is zero.

Files

     None.

Particulars

     IRFNUM is supplied as a convenience, to allow users to refer to
     the various standard inertial reference frames by name.

Examples

     In the following example, the rotation from DE-118 to FK4 is
     computed without knowing the indices of these frames.

        CALL IRFNUM ( 'DE-118', A )
        CALL IRFNUM ( 'FK4',    B )

        CALL IRFROT ( A, B, ROTAB )

     IRFNUM can be used to rotate vectors into the default frame,
     as illustrated by the following code fragment.

        CALL IRFNUM ( 'FK4',     A )
        CALL IRFNUM ( 'DEFAULT', B )

        CALL IRFROT ( A, B, ROTAB                 )
        CALL MXV    (       ROTAB, OLDVEC, NEWVEC )

Restrictions

     None.

Literature_References

     See subroutine CHGIRF.

Author_and_Institution

     B.V. Semenov    (JPL)
     W.L. Taber      (JPL)
     I.M. Underwood  (JPL)
     E.D. Wright     (JPL)

Version

    SPICELIB Version 4.3.0, 24-SEP-2013 (BVS)

        Updated to treat J2000 as a special case and to not
        CHKIN/CHOUT to increase efficiency.

    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 signalled 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)
Wed Apr  5 17:46:47 2017