def compute_bounds(values):
    """
    return bounding box for list of offsets
    """
    i = [value[0] for value in values]
    j = [value[1] for value in values]
    k = [value[2] for value in values]
    bounds = lambda offsets: (min(offsets), max(offsets))
    return (bounds(i), bounds(j), bounds(k))