text: /*
  
  -Procedure  vhat_c ( "V-Hat", unit vector along V, 3 dimensions )
  
  -Abstract
  
     Find the unit vector along a double precision 3-dimensional vector.
  
  -Disclaimer
  
     THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE
     CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S.
     GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE
     ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE
     PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS"
     TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY
     WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A
     PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC
     SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE
     SOFTWARE AND RELATED MATERIALS, HOWEVER USED.
  
     IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA
     BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT
     LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND,
     INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS,
     REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE
     REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY.
  
     RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF
     THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY
     CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE
     ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE.
  
  -Required_Reading
  
     None.
  
  -Keywords
  
     VECTOR
  
  */
  
     #include <math.h>
     #include "SpiceUsr.h"
     #undef    vhat_c
  
  
     void vhat_c ( ConstSpiceDouble  v1  [3], 
                   SpiceDouble       vout[3] )
  /*
  
  -Brief_I/O
  
     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     v1         I   Vector to be unitized.
     vout       O   Unit vector v1 / |v1|.
  
  -Detailed_Input
  
      v1            This is any double precision, 3-dimensional vector.
  
  -Detailed_Output
  
      vout          vout contains the unit vector in the direction of v1.
                    If v1 represents the zero vector, then vout will also
                    be the zero vector.  vout may overwrite v1.
  
  -Parameters
  
     None.
  
  -Exceptions
  
     Error free.
  
     If v1 represents the zero vector, then vout will also be the zero
     vector.
  
  -Files
  
     None.
  
  -Particulars
  
     vhat_c determines the magnitude of v1 and then divides each
     component of v1 by the magnitude.  This process is highly stable
     over the whole range of 3-dimensional vectors.
  
  -Examples
  
     The following table shows how v1 maps to vout.
  
     v1                        vout
     ------------------        ------------------
     ( 5,     12,    0     )   ( 5/13, 12/13, 0   )
     ( 1.e-7, 2.e-7, 2.e-7 )   ( 1/3,  2/3,   2/3 )
  
  
  -Restrictions
  
     None.
  
     There is no known case whereby floating point overflow may occur.
     Thus, no error recovery or reporting scheme is incorporated
     into this subroutine.
  
  -Literature_References
  
     None.
  
  -Author_and_Institution
  
     N.J. Bachman       (JPL)
     W.L. Taber         (JPL)
     W.M. Owen          (JPL)
  
  -Version
  
     -CSPICE Version 1.0.2, 16-JAN-2008   (EDW)
  
        Corrected typos in header titles:
        
        Detailed Input to Detailed_Input
        Detailed Output to Detailed_Output
        
     -CSPICE Version 1.0.1, 12-NOV-2006 (EDW)
  
        Added Parameters section header.
  
     -CSPICE Version 1.0.0, 16-APR-1999 (EDW)
  
  -Index_Entries
  
     unitize a 3-dimensional vector
  
  -&
  */
  
  {  /* Begin vhat_c */
  
  
     /*
     Local variables
     */
     SpiceDouble                        vmag;
  
  
     /*
     Obtain the magnitude of v1.
     */
     vmag = vnorm_c(v1);
  
     /*
     If vmag is nonzero, then unitize.  Note that this process is
     numerically stable: overflow could only happen if vmag were small,
     but this could only happen if each component of v1 were small.
     In fact, the magnitude of any vector is never less than the
     magnitude of any component.
     */
  
     if ( vmag > 0.0 )
        {
        vout[0] = v1[0] / vmag;
        vout[1] = v1[1] / vmag;
        vout[2] = v1[2] / vmag;
        }
     else
        {
        vout[0] = 0.0;
        vout[1] = 0.0;
        vout[2] = 0.0;
        }
  
  
  } /* End vhat_c */
  