The Vector handle is a directed arrow radiating from an origin.  This
is used to interactively choose a direction from an interactively
chosen origin.  

Parameters:

    input       - A group field.  The centroid of this group is used
                  as the default origin.
    onoff       - Whether the handle is enabled, 1 means enable.
    scale       - A global scale defined by the handle.  This is
                  defined by dragging the red tip of the handle arrow.
    twist       - The amount to twist around the given direction.
                  This is controlled by dragging the circle at the end
                  of the arrow.  It gives the total twist in degrees.
    tx, ty, tz  - The origin of the arrow.
    vx, vy, vz  - The normalized direction in which the arrow points.

See Also: Angle, Bounding Box Vector, Project
