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Index Page vpack_c

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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

       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

#### Link to routine vpack_c source file vpack_c.c

    Fri Dec 31 18:41:15 2021