How to use the compas.geometry.basic.cross_vectors function in compas

p = len(polygon)

    assert p > 2, "At least three points required"

    if p == 3:
        return centroid_points(polygon)

    cx, cy, cz = 0.0, 0.0, 0.0
    A2 = 0

    o = centroid_points(polygon)
    a = polygon[-1]
    b = polygon[0]
    oa = subtract_vectors(a, o)
    ob = subtract_vectors(b, o)
    n0 = cross_vectors(oa, ob)

    x, y, z = centroid_points([o, a, b])
    a2 = length_vector(n0)

    A2 += a2
    cx += a2 * x
    cy += a2 * y
    cz += a2 * z

    for i in range(1, len(polygon)):
        a = b
        b = polygon[i]

        oa = ob
        ob = subtract_vectors(b, o)

Examples
    --------
    >>> triangle = [1.0, 0, 0], [-1.0, 0, 0], [0, 0, 1.0]
    >>> line = [-1, 1, 0], [-0.5, 0.5, 0]
    >>> reflect_line_triangle(line, triangle)
    ([0.0, 0.0, 0.0], [1.0, 1.0, 0.0])

    """
    x = intersection_line_triangle(line, triangle, tol=tol)
    if not x:
        return

    a, b = line
    t1, t2, t3 = triangle
    ab = subtract_vectors(b, a)
    n = cross_vectors(subtract_vectors(t2, t1), subtract_vectors(t3, t1))

    if dot_vectors(ab, n) > 0:
        # the line does not point towards the front of the triangle
        return

    mirror = x, add_vectors(x, n)
    return x, mirror_point_line(a, mirror)

def _normal_face(face):
        u = subtract_vectors(points[face[1]], points[face[0]])
        v = subtract_vectors(points[face[-1]], points[face[0]])
        return cross_vectors(u, v)

tol : float, optional
        A tolerance for membership verification.
        Default is ``1e-6``.

    Returns
    -------
    point : tuple
        The intersectin point.
    None
        If the intersection does not exist.

    """
    a, b, c = triangle
    ab = subtract_vectors(b, a)
    ac = subtract_vectors(c, a)
    n = cross_vectors(ab, ac)
    plane = a, n

    x = intersection_line_plane(line, plane, tol=tol)

    if x:
        if is_point_in_triangle(x, triangle):
            return x

Examples
    --------
    >>> xaxis = [1, 4, 5]
    >>> yaxis = [1, 0, -2]
    >>> xaxis, yaxis = orthonormalize_axes(xaxis, yaxis)
    >>> allclose(xaxis, [0.1543, 0.6172, 0.7715], tol=0.001)
    True
    >>> allclose(yaxis, [0.6929, 0.4891, -0.5298], tol=0.001)
    True
    """
    xaxis = normalize_vector(xaxis)
    yaxis = normalize_vector(yaxis)
    zaxis = cross_vectors(xaxis, yaxis)
    if not norm_vector(zaxis):
        raise ValueError("Xaxis and yaxis cannot span a plane.")
    yaxis = cross_vectors(normalize_vector(zaxis), xaxis)
    return xaxis, yaxis

"""
    o = centroid_points(polygon)
    a = polygon[-1]
    b = polygon[0]
    oa = subtract_vectors(a, o)
    ob = subtract_vectors(b, o)

    n0 = cross_vectors(oa, ob)

    area = 0.5 * length_vector(n0)

    for i in range(0, len(polygon) - 1):
        oa = ob
        b = polygon[i + 1]
        ob = subtract_vectors(b, o)
        n = cross_vectors(oa, ob)

        if dot_vectors(n, n0) > 0:
            area += 0.5 * length_vector(n)
        else:
            area -= 0.5 * length_vector(n)

    return area

points are different.
        If the lines are parallel, the return value is [None, None].

    Examples
    --------
    >>>

    """
    a, b = l1
    c, d = l2

    ab = subtract_vectors(b, a)
    cd = subtract_vectors(d, c)

    n = cross_vectors(ab, cd)
    n1 = normalize_vector(cross_vectors(ab, n))
    n2 = normalize_vector(cross_vectors(cd, n))

    plane_1 = (a, n1)
    plane_2 = (c, n2)

    i1 = intersection_line_plane(l1, plane_2, tol=tol)
    i2 = intersection_line_plane(l2, plane_1, tol=tol)

    return i1, i2

If the lines are skewed and thus only have an apparent intersection, the two
        points are different.
        If the lines are parallel, the return value is [None, None].

    Examples
    --------
    >>>

    """
    a, b = l1
    c, d = l2

    ab = subtract_vectors(b, a)
    cd = subtract_vectors(d, c)

    n = cross_vectors(ab, cd)
    n1 = normalize_vector(cross_vectors(ab, n))
    n2 = normalize_vector(cross_vectors(cd, n))

    plane_1 = (a, n1)
    plane_2 = (c, n2)

    i1 = intersection_line_plane(l1, plane_2, tol=tol)
    i2 = intersection_line_plane(l2, plane_1, tol=tol)

    return i1, i2

def local_axes(a, b, c):
    u = b - a
    v = c - a
    w = cross_vectors(u, v)
    v = cross_vectors(w, u)
    return normalize_vector(u), normalize_vector(v), normalize_vector(w)