Procedure

   vhat_c ( "V-Hat", unit vector along V, 3 dimensions ) 

   void vhat_c ( ConstSpiceDouble  v1  [3],
                 SpiceDouble       vout[3] )

Abstract

   Find the unit vector along a double precision 3-dimensional vector.

Required_Reading

   None.

Keywords

   VECTOR

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   v1         I   Vector to be unitized.
   vout       O   Unit vector v1 / |v1|.

Detailed_Input

   v1          is any double precision, 3-dimensional vector.

Detailed_Output

   vout        is 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.

   1)  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 numerical results shown for this example may differ across
   platforms. The results depend on the SPICE kernels used as
   input, the compiler and supporting libraries, and the machine
   specific arithmetic implementation.

   1) Define a set of vectors and compute their corresponding unit
      vector.


      Example code begins here.


      /.
         Program vhat_ex1
      ./
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main( )
      {

         /.
         Local parameters.
         ./
         #define SETSIZ       2

         /.
         Local variables.
         ./
         SpiceDouble          vout   [3];

         SpiceInt             i;

         /.
         Define the vector set.
         ./
         SpiceDouble          seta   [SETSIZ][3] = {
                                   {5.0,  12.0,  0.0},
                                   {1.e-7,  2.e-7, 2.e-7} };

         /.
         Calculate the unit vectors.
         ./
         for ( i = 0; i < SETSIZ; i++ )
         {

            vhat_c ( seta[i], vout );

            printf( "Vector     :  %12.8f %12.8f %12.8f\n",
                         seta[i][0], seta[i][1], seta[i][2] );
            printf( "Unit vector:  %12.8f %12.8f %12.8f\n",
                                  vout[0], vout[1], vout[2] );
            printf( " \n" );

         }

         return ( 0 );
      }


      When this program was executed on a Mac/Intel/cc/64-bit
      platform, the output was:


      Vector     :    5.00000000  12.00000000   0.00000000
      Unit vector:    0.38461538   0.92307692   0.00000000

      Vector     :    0.00000010   0.00000020   0.00000020
      Unit vector:    0.33333333   0.66666667   0.66666667

Restrictions

   1)  There is no known case whereby floating point overflow may
       occur. Thus, no error recovery or reporting scheme is
       incorporated into this routine.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   W.M. Owen           (JPL)
   W.L. Taber          (JPL)
   E.D. Wright         (JPL)

Version

   -CSPICE Version 1.0.3, 10-AUG-2021 (JDR)

       Edited the header to comply with NAIF standard. Added
       complete code example to -Examples section.

   -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) (WMO) (WLT) (NJB)

Index_Entries

   unitize a 3-dimensional vector