CONTOUR3 3-D contour plot.
    CONTOUR3(...) is the same as CONTOUR(...) except that the contours
    are drawn at their corresponding Z level.

    C = CONTOUR3(...) returns contour matrix C as described in CONTOURC
    and used by CLABEL.

    [C,H] = CONTOUR3(...) returns a column vector H of handles to PATCH
    objects. The UserData property of each object contains the height
    value for each contour.

    Example:
       contour3(peaks)