pxform_c

Index Page pxform_c
A B C D E F G H I J K L M N O P Q R S T U V W X
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       void pxform_c ( ConstSpiceChar   * from,
                       ConstSpiceChar   * to,
                       SpiceDouble        et,
                       SpiceDouble        rotate[3][3] )
#### Abstract
       Return the matrix that transforms position vectors from one
       specified frame to another at a specified epoch.
#### Required_Reading
       FRAMES
#### Keywords
       FRAMES
#### 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 a 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 of 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.

          #include "SpiceUsr.h"
                .
                .
                .
          bodvcd_c ( 399, radii, 3, &n, abc );

          equatr   =  abc[0];
          polar    =  abc[2];
          f        =  ( equatr - polar ) / equatr;

          georec_c ( long,        lat,      0.0,   equatr,   f,   epos );
          pxform_c ( "IAU_EARTH", "J2000",  et,    rotate              );
          mxv_c    (  rotate,   epos,     jpos                         );

       The position 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
       -CSPICE Version 1.0.4, 27-FEB-2008 (BVS)

           Added FRAMES to the Required_Reading section of the header.

       -CSPICE Version 1.0.3, 24-OCT-2005 (NJB)

           Header updates: example had invalid flattening factor
           computation; this was corrected.  Reference to bodvar_c was
           replaced with reference to bodvcd_c.

       -CSPICE Version 1.0.2, 07-JAN-2004 (EDW)

           Trivial typo correction to example section.

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

           Various header corrections were made.

       -CSPICE Version 1.0.0, 20-JUN-1999 (NJB) (WLT)
#### Index_Entries
       Find a position transformation matrix
#### Link to routine pxform_c source file pxform_c.c

    Thu Apr 16 08:58:53 2009