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实践教程 | 我竟然用 OpenCV 实现了卡尔曼滤波
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作者 | gloomyfish
来源 | OpenCV学堂
编辑 | 极市平台

卡尔曼滤波原理

卡尔曼滤波最早可以追溯到Wiener滤波,不同的是卡尔曼采用状态空间来描述它的滤波器,卡尔曼滤波器同时具有模糊/平滑与预测功能,特别是后者在视频分析与对象跟踪应用场景中被发扬光大,在离散空间(图像或者视频帧)使用卡尔曼滤波器相对简单。假设我们根据一个处理想知道一个变量值如下:

最终卡尔曼滤波完整的评估与空间预测模型工作流程如下:

OpenCV API

cv::KalmanFilter::KalmanFilter(
    int dynamParams, 
    int measureParams,
    int controlParams = 0,
    int type = CV_32F 
)
# dynamParams表示state的维度
# measureParams表示测量维度
# controlParams表示控制向量
# type表示创建的matrices

代码演示

import cv2
from math import cos, sin, sqrt
import numpy as np

if __name__ == "__main__":

    img_height = 500
    img_width = 500
    kalman = cv2.KalmanFilter(2, 1, 0)

    cv2.namedWindow("Kalman", cv2.WINDOW_AUTOSIZE)

    while True:
        state = 0.1 * np.random.randn(2, 1)

        # 初始化
        kalman.transitionMatrix = np.array([[1., 1.], [0., 1.]])
        kalman.measurementMatrix = 1. * np.ones((1, 2))
        kalman.processNoiseCov = 1e-5 * np.eye(2)
        kalman.measurementNoiseCov = 1e-1 * np.ones((1, 1))
        kalman.errorCovPost = 1. * np.ones((2, 2))
        kalman.statePost = 0.1 * np.random.randn(2, 1)

        while True:
            def calc_point(angle):
                return (np.around(img_width/2 + img_width/3*cos(angle), 0).astype(int),
                        np.around(img_height/2 - img_width/3*sin(angle), 1).astype(int))

            state_angle = state[0, 0]
            state_pt = calc_point(state_angle)
            # 预测
            prediction = kalman.predict()
            predict_angle = prediction[0, 0]
            predict_pt = calc_point(predict_angle)

            measurement = kalman.measurementNoiseCov * np.random.randn(1, 1)

            # 生成测量
            measurement = np.dot(kalman.measurementMatrix, state) + measurement
            measurement_angle = measurement[0, 0]
            measurement_pt = calc_point(measurement_angle)

            # plot points
            def draw_cross(center, color, d):
                cv2.line(img,
                         (center[0] - d, center[1] - d), (center[0] + d, center[1] + d),
                         color, 1, cv2.LINE_AA, 0)
                cv2.line(img,
                         (center[0] + d, center[1] - d), (center[0] - d, center[1] + d),
                         color, 1, cv2.LINE_AA, 0)

            img = np.zeros((img_height, img_width, 3), np.uint8)

            cv2.line(img, state_pt, measurement_pt, (0, 0, 255), 3, cv2.LINE_AA, 0)
            cv2.line(img, state_pt, predict_pt, (255, 0, 0), 3, cv2.LINE_AA, 0)

            # 校正预测与测量值差异
            kalman.correct(measurement)

            # 更新noise矩阵与状态
            process_noise = sqrt(kalman.processNoiseCov[0,0]) * np.random.randn(2, 1)
            state = np.dot(kalman.transitionMatrix, state) + process_noise

            cv2.imshow("Kalman", img)

            code = cv2.waitKey(100)
            if code != -1:
                break

        if code in [27, ord('q'), ord('Q')]:
            break

    cv2.destroyWindow("Kalman")

—END —

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