import math


def characteristic_dimension(bb):
    """ Returns the length of the bounding box diagonal
    """

    x1,y1,z1 = bb[0]
    x2,y2,z2 = bb[1]

    return math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2))