[OpenCV] Optical flow

#include <opencv2/highgui/highgui.hpp>

#include <opencv2/imgproc/imgproc.hpp>

#include <opencv2/calib3d/calib3d.hpp>

#include <opencv2/features2d/features2d.hpp>

#include <iostream>

#include <algorithm>




int main()

{

// video file cap

cv::VideoCapture input("cars.mp4");




cv::Mat img, img_gray;




// feature detect

cv::OrbFeatureDetector detector(5000);

std::vector<cv::KeyPoint> img_keypoints, car_keypoints;

cv::Mat img_descriptors, car_descriptors;




// car image read

input.read(img);

cv::Mat car;

img(cv::Rect(720, 320, 150, 100)).copyTo(car);




detector(car, cv::Mat(), car_keypoints, car_descriptors);

drawKeypoints(car, car_keypoints, car);




for (;;)

{

if (!input.read(img))

break;




detector(img, cv::Mat(), img_keypoints, img_descriptors);

drawKeypoints(img, img_keypoints, img);




cv::BFMatcher matcher;

std::vector< cv::DMatch > matches;

matcher.match(car_descriptors, img_descriptors, matches);




std::vector<cv::Point2f> car_points, img_points;

for (int i = 0; i < matches.size(); i++)

{

car_points.push_back(car_keypoints[matches[i].queryIdx].pt);

img_points.push_back(img_keypoints[matches[i].trainIdx].pt);

}

// find homography

cv::Matx33f H = cv::findHomography(car_points, img_points, CV_RANSAC);




std::vector<cv::Point> car_border, img_border;

car_border.push_back(cv::Point(0, 0));

car_border.push_back(cv::Point(0, car.rows));

car_border.push_back(cv::Point(car.cols, car.rows));

car_border.push_back(cv::Point(car.cols, 0));




for (size_t i = 0; i < car_border.size(); i++)

{

cv::Vec3f p = H * cv::Vec3f(car_border[i].x, car_border[i].y, 1);

img_border.push_back(cv::Point(p[0] / p[2], p[1] / p[2]));

}




cv::polylines(img, img_border, true, CV_RGB(0, 255, 0));




cv::Mat img_matches;

cv::drawMatches(car, car_keypoints, img, img_keypoints,

matches, img_matches);




cv::imshow("img_matches", img_matches);

char c = cv::waitKey(30);




if (c == 27) // 27 is ESC code

break;

}

}