Procedure

   void sxform_c ( ConstSpiceChar  * from, 
                   ConstSpiceChar  * to, 
                   SpiceDouble       et, 
                   SpiceDouble       xform[6][6] ) 

Abstract

 
   Return the state transformation matrix from one 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 state transformation matrix.
   xform      O   A state transformation matrix.
 

Detailed_Input

 
   from        is the name of a reference frame in which a state is
               known.
 
   to          is the name of a reference frame in which it is desired
               to represent the state.
 
   et          is the epoch in ephemeris seconds past the epoch of
               J2000 (TDB) at which the state transformation matrix
               should be evaluated.

Detailed_Output

 
   xform       is the matrix that transforms states from the reference
               frame `from' to the frame `to' at epoch `et'. If (x, y,
               z, dx, dy, dz) is a state relative to the frame `from'
               then the vector ( x', y', z', dx', dy', dz' ) is the
               same state relative to the frame `to' at epoch `et'.
               Here the vector ( x', y', z', dx', dy', dz' ) is defined
               by the equation:
 
                  -   -       -          -     -  - 
                 | x'  |     |            |   | x  | 
                 | y'  |     |            |   | y  | 
                 | z'  |  =  |   xform    |   | z  | 
                 | dx' |     |            |   | dx | 
                 | dy' |     |            |   | dy | 
                 | dz' |     |            |   | dz | 
                  -   -       -          -     -  - 
 

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 for computing 
   state 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 state 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) state of this station.  The following code fragment 
   illustrates how to transform the position of the station to 
   a J2000 state. 
 
      #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,  estate ); 
 
      estate[3] = 0.0; 
      estate[4] = 0.0; 
      estate[5] = 0.0; 
 
      sxform_c ( "IAU_EARTH", "J2000",   et,    xform  ); 
      mxvg_c   (  xform,       estate,   6,  6, jstate ); 
 
   The state `jstate' is the desired J2000 state 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 1.1.3, 27-FEB-2008 (BVS)

       Added FRAMES to the Required_Reading section of the header.

   -CSPICE Version 1.1.2, 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 1.1.1, 03-JUL-2003 (NJB) (CHA)

       Various header corrections were made.
   
   -CSPICE Version 1.1.0, 08-FEB-1998 (NJB)  
   
       References to C2F_CreateStr_Sig were removed; code was
       cleaned up accordingly.  String checks are now done using
       the macro CHKFSTR.
       
   -CSPICE Version 1.0.0, 25-OCT-1997 (NJB)
   
      Based on SPICELIB Version 1.0.0, 19-SEP-1995 (WLT)

Index_Entries

 
   Find a state transformation matrix 
 

Link to routine sxform_c source file sxform_c.c