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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

      PXFORM ( Position Transformation Matrix )
 
      SUBROUTINE PXFORM ( FROM, TO, ET, ROTATE )
 

Abstract

     Return the matrix that transforms position vectors from one
     specified frame to another at a specified epoch.

Required_Reading

      FRAMES

Keywords

      FRAMES

Declarations

 
      IMPLICIT NONE

      INCLUDE               'zzctr.inc'

      CHARACTER*(*)         FROM
      CHARACTER*(*)         TO
      DOUBLE PRECISION      ET
      DOUBLE PRECISION      ROTATE  ( 3, 3 )
 

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     FROM       I   Name of the frame to transform from.
     TO         I   Name of the frame to transform to.
     ET         I   Epoch of the rotation matrix.
     ROTATE     O   A rotation matrix

Detailed_Input

     FROM        is the name of some reference frame in which
                 a position vector is known.

     TO          is the name of a reference frame in which it
                 is desired to represent a position vector.

     ET          is the epoch in ephemeris seconds past the epoch
                 of J2000 (TDB) at which the position transformation
                 matrix ROTATE should be evaluated.

Detailed_Output

     ROTATE      is the matrix that transforms position vectors from
                 the reference frame FROM to the frame TO at epoch ET.
                 If (x, y, z) is a position relative to the frame FROM
                 then the vector ( x', y', z') is the same position
                 relative to the frame TO at epoch ET.  Here the
                 vector ( x', y', z' ) is defined by the equation:

                   -   -       -        -     -  -
                  | x'  |     |          |   | x  |
                  | y'  |     |  ROTATE  |   | y  |
                  | z'  |  =  |          |   | z  |
                   -   -       -        -     -  -

Parameters

     None.

Exceptions

     1) If sufficient information has not been supplied via loaded
        SPICE kernels to compute the transformation between the
        two frames, the error will be diagnosed by a routine
        in the call tree to this routine.

     2) If either frame FROM or TO is not recognized the error
        'SPICE(UNKNOWNFRAME)' will be signaled.

Files

     None.

Particulars

     This routine provides the user level interface to computing
     position transformations from one reference frame to another.

     Note that the reference frames may be inertial or non-inertial.
     However, the user must take care that sufficient SPICE kernel
     information is loaded to provide a complete position
     transformation path from the FROM frame to the TO frame.

Examples

     Suppose that you have geodetic coordinates of a station on the
     surface of the earth and that you need the inertial (J2000)
     position of this station.  The following code fragment
     illustrates how to transform the position of the station to a
     J2000 position.

        CALL BODVRD ( 'EARTH', RADII, 3, N, ABC  )

        EQUATR   =  ABC(1)
        POLAR    =  ABC(3)
        F        = (EQUATR - POLAR) / EQUATR

        CALL GEOREC ( LONG, LAT, 0.0D0,  EQUATR, F, EPOS )

        CALL PXFORM ( 'IAU_EARTH', 'J2000', ET,  ROTATE  )
        CALL MXV    (  ROTATE,      EPOS,   JPOS         )

     The state JPOS is the desired J2000 position of the station.

Restrictions

     None.

Literature_References

      None.

Author_and_Institution

     C.H. Acton      (JPL)
     N.J. Bachman    (JPL)
     B.V. Semenov    (JPL)
     W.L. Taber      (JPL)

Version

    SPICELIB Version 1.1.0, 23-SEP-2013 (BVS) 

        Updated to save the input frame names and POOL state counters
        and to do frame name-ID conversions only if the counters have
        changed.

    SPICELIB Version 1.0.3, 27-FEB-2008 (BVS) 

        Added FRAMES to the Required_Reading section.

    SPICELIB Version 1.0.2, 23-OCT-2005 (NJB) 

        Header example had invalid flattening factor computation;
        this was corrected.  Reference to BODVAR in header was 
        replaced with reference to BODVRD.

    SPICELIB Version 1.0.1, 29-JUL-2003 (NJB) (CHA)

        Various header corrections were made.

    SPICELIB Version 1.0.0, 05-APR-1999 (WLT)
Wed Apr  5 17:47:06 2017