Procedure

   vpack_c ( Pack three scalar components into a vector ) 

   void vpack_c ( SpiceDouble   x,
                  SpiceDouble   y,
                  SpiceDouble   z,
                  SpiceDouble   v[3] )

Abstract

   Pack three scalar components into a vector.

Required_Reading

   None.

Keywords

   VECTOR

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   x,
   y,
   z          I   Scalar components of a vector.
   v          O   Equivalent vector.

Detailed_Input

   x,
   y,
   z           are the scalar components of a 3-dimensional vector.

Detailed_Output

   v           is the equivalent vector, such that

                  v[0] = x
                  v[1] = y
                  v[2] = z

Parameters

   None.

Exceptions

   Error free.

Files

   None.

Particulars

   Basically, this is just shorthand notation for the common
   sequence

      v[0] = x;
      v[1] = y;
      v[2] = z;

   The routine is useful largely for two reasons. First, it
   reduces the chance that the programmer will make a "cut and
   paste" mistake, like

      v[0] = x;
      v[0] = y;
      v[0] = z;

   Second, it makes conversions between equivalent units simpler,
   and clearer. For instance, the sequence

      v[0] = x * rpd_c();
      v[1] = y * rpd_c();
      v[2] = z * rpd_c();

   can be replaced by the (nearly) equivalent sequence

      vpack_c ( x, y, z,    v );
      vscl_c  ( rpd_c(), v, v );

Examples

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

   1) Compute an upward normal of an equilateral triangle lying
      in the x-y plane and centered at the origin.


      Example code begins here.


      /.
         Program vpack_ex1
      ./
      #include <math.h>
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main( )
      {

         /.
         Local variables
         ./
         SpiceDouble          normal [3];
         SpiceDouble          s;
         SpiceDouble          v1     [3];
         SpiceDouble          v2     [3];
         SpiceDouble          v3     [3];

         s = sqrt(3.0)/2;

         /.
         Define the three corners of the triangle.
         ./
         vpack_c (   s, -0.5, 0.0, v1 );
         vpack_c ( 0.0,  1.0, 0.0, v2 );
         vpack_c (  -s, -0.5, 0.0, v3 );

         /.
         Compute an upward normal of the triangle.
         ./
         pltnrm_c ( v1, v2, v3, normal );

         printf( "NORMAL =  %16.13f %16.13f %16.13f\n",
                        normal[0], normal[1], normal[2] );

         return ( 0 );
      }


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


      NORMAL =   0.0000000000000  0.0000000000000  2.5980762113533

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   I.M. Underwood      (JPL)

Version

   -CSPICE Version 1.0.1, 16-JUL-2020 (JDR)

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

   -CSPICE Version 1.0.0, 24-MAY-1999 (IMU) (NJB)

Index_Entries

   pack three scalar components into a vector