Procedure

     VDIST ( Vector distance )

     DOUBLE PRECISION FUNCTION  VDIST ( V1, V2 )

Abstract

     Return the distance between two three-dimensional vectors.

Required_Reading

     None.

Keywords

     VECTOR

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION      V1 ( 3 )
     DOUBLE PRECISION      V2 ( 3 )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------

     V1,
     V2         I   Two 3-vectors.

     The function returns the distance between V1 and V2.

Detailed_Input

     V1,
     V2       are two vectors in three-dimensional space, the
              distance between which is desired.

Detailed_Output

     The function returns the distance between V1 and V2. This is
     defined as

        ||  V1 - V2  ||,

     where || x || indicates the Euclidean norm of the vector x.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     This function is simply shorthand for the code

        CALL VSUB ( V1, V2, DIFF )

        DIST = VNORM ( DIFF )

     Using this function saves you the annoyance of declaring local
     storage for the difference vector DIFF.


     The Euclidean norm of a three-dimensional vector (x, y, z) is
     defined as

                                     1/2
             2        2        2
        (   x    +   y    +   z    ).


     This number is the distance of the point (x, y, z) from the
     origin. If A and B are two vectors whose components are

        ( A(1), A(2), A(3) )    and    ( B(1), B(2), B(3) ),

     then the distance between A and B is the norm of the difference
     A - B, which has components


        (  A(1) - B(1),  A(2) - B(2),  A(3) - B(3)  ).


     A related routine is VDISTG, which computes the distance between
     two vectors of general dimension.

Examples

     1)  If V1 is

            ( 2.0D0,  3.0D0,  0.D0 )

         and V2 is

            ( 5.0D0,  7.0D0,  12.D0 ),

         VDIST (V1, V2) will be 13.D0.


     2)  If VGR2 and NEP are states of the Voyager 2 spacecraft and
         Neptune with respect to some common center at a given time
         ET, then

            VDIST ( VGR2, NEP )

         yields the distance between the spacecraft and Neptune at time
         ET.

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (JPL)

Version

    SPICELIB Version 1.1.0, 25-MAY-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    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, 08-JUL-1990 (NJB)