Procedure

     VPACK ( Pack three scalar components into a vector )

     SUBROUTINE VPACK ( X, Y, Z, V )

Abstract

     Pack three scalar components into a vector.

Required_Reading

     None.

Keywords

     VECTOR

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION X
     DOUBLE PRECISION Y
     DOUBLE PRECISION Z
     DOUBLE PRECISION V ( 3 )

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(1) = X
                 V(2) = Y
                 V(3) = Z

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     Basically, this is just shorthand notation for the common
     sequence

        V(1) = X
        V(2) = Y
        V(3) = 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(1) = X
        V(1) = Y
        V(1) = Z

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

        V(1) = X * RPD
        V(2) = Y * RPD
        V(3) = Z * RPD

     can be replaced by the (nearly) equivalent sequence

        CALL VPACK  ( X,   Y, Z, V )
        CALL VSCLIP ( RPD, 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
              IMPLICIT NONE

        C
        C     Local variables
        C
              DOUBLE PRECISION      NORMAL ( 3 )
              DOUBLE PRECISION      S
              DOUBLE PRECISION      V1     ( 3 )
              DOUBLE PRECISION      V2     ( 3 )
              DOUBLE PRECISION      V3     ( 3 )


              S = SQRT(3.D0)/2

        C
        C     Define the three corners of the triangle.
        C
              CALL VPACK (    S,  -0.5D0,  0.D0, V1 )
              CALL VPACK ( 0.D0,    1.D0,  0.D0, V2 )
              CALL VPACK (   -S,  -0.5D0,  0.D0, V3 )

        C
        C     Compute an upward normal of the triangle.
        C
              CALL PLTNRM ( V1, V2, V3, NORMAL )

              WRITE (*, '(A,3F17.13)' ) 'NORMAL = ', NORMAL

              END


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


        NORMAL =   0.0000000000000  0.0000000000000  2.5980762113533

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.1.0, 16-JUL-2020 (JDR)

        Added IMPLICIT NONE statement.

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

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (IMU)