Rotate Y

def rotate_y(vert, theta=60):
    sin_theta = np.sin(theta)
    cos_theta = np.cos(theta)
    vertex = vert.copy()
    vertex[:,0] = vert[:,0] * cos_theta + vert[:,2] * sin_theta
    vertex[:,2] = vert[:,2] * cos_theta - vert[:,0] * sin_theta
    return vertex