Example of simple geometric transformation on a sequence of 2D points.

import cv2
import numpy as np
from matplotlib import pyplot as plt
import matplotlib.lines as mlines


points = np.array([[4,10], [7,8], [10,5], [9,9], [13,9], [15,10]], dtype=np.float32)


def plot(points):
    plt.axis([0, 20, 0, 20])

    plt.gca().add_line(mlines.Line2D([0, 20], [10, 10]))
    plt.gca().add_line(mlines.Line2D([10, 10], [0, 20]))
    plt.gca().add_line(mlines.Line2D([0, 20], [0, 20]))
    plt.gca().add_line(mlines.Line2D([20, 0], [0, 20]))
    plt.gca().invert_yaxis()

    plt.scatter(points[:,0], points[:,1], marker='o', c='r')
    for point in points:
        plt.gca().annotate('(%d,%d)' % tuple(point) , tuple(point + (0.3,-0.3)))


m_1 = cv2.getRotationMatrix2D((10,10), -45, 1.0)
m_2 = cv2.getRotationMatrix2D((10,10), 45, 1.0)

rot_1 = cv2.transform(points.reshape(-1,1,2), m_1).reshape(-1,2)
rot_2 = cv2.transform(points.reshape(-1,1,2), m_2).reshape(-1,2)

plt.figure(1)
plt.subplot(131)
plot(points)
plt.subplot(132)
plot(rot_1)
plt.subplot(133)
plot(rot_2)
plt.show()