Table of contents
IRFNUM ( Inertial reference frame number )
ENTRY IRFNUM ( NAME, INDEX )
Return the index of one of the standard inertial reference
frames supported by IRFROT.
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
NAME I Name of standard inertial reference frame.
INDEX O Index of frame.
NAME is the name of one of the standard inertial
reference frames supported by IRFROT, or
INDEX is the index of the frame specified by NAME.
1) If NAME is not recognized, INDEX is zero.
2) If no default frame has been specified, INDEX is zero.
IRFNUM is supplied as a convenience, to allow users to refer to
the various standard inertial reference frames by name.
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 )
 J. Lieske, "Precession Matrix Based on IAU (1976) System of
Astronomical Constants," Astron. Astrophys. 73, 282-284,
 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.
 E. M. Standish, Jr., "Conversion of Ephemeris Coordinates
from the B1950 System to the J2000 System," JPL IOM
314.6-581, 24 June 1985.
 E. M. Standish, Jr., "The Equinox Offsets of the JPL
Ephemeris," JPL IOM 314.6-929, 26 February 1988.
 J. Lieske, "Expressions for the Precession Quantities Based
upon the IAU (1976) System of Astronomical Constants,"
Astron. Astrophys. 58, 1-16, 1977.
 L. Bass and R. Cesarone, "Mars Observer Planetary Constants
and Models," JPL D-3444, November 1990.
 P. Kenneth Seidelmann (Ed.), "Explanatory Supplement to the
Astronomical Almanac," University Science Books, 1992.
J. Diaz del Rio (ODC Space)
B.V. Semenov (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
E.D. Wright (JPL)
SPICELIB Version 4.4.0, 17-JUN-2021 (JDR)
Added IMPLICIT NONE statement.
Edited the header to comply with NAIF standard. Added
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 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
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 .
The frame MARSIAU was added to the list
of recognized frames. This is the standard mars
referenced inertial frame used by the Mars Observer
Values for the obliquity of the ecliptic were taken
from the Explanatory Supplement  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)