跟踪或记录物体的位置

Question

当一个人在房间里将一个物体从一个地方移动到另一个地方时，用相机跟踪或记录它的位置。这使得房间看起来像一个自动仓库，因为它记录了物体的位置，即使它们被人移动了。我不知道该怎么做。

Answer 1

如果知道物体的初始位置，就可以使用光流来判断物体是否移动。

看看 Lucas-Kanade 方法。 OpenCV也有实现

    cv::Mat prev_gray, curr_gray; //previous and current frame
    std::vector<cv::Point2f> features_prev, features_next;
    std::vector<uchar> status;
    std::vector<float> err;

将研究对象的点存储在 features_prev 中。如果你想连续监控，那么你可以跟踪当前和之前的帧，以及特征点

    cv::calcOpticalFlowPyrLK(prev_gray, curr_gray, features_prev, features_next, status, err);
    prev_gray = curr_gray.clone();
    features_prev.swap(features_next);
    features_prev.clear();

如果物体被移动了，你可以从 features_next 中知道这些点被移动到了哪里。

Answer 2

查看新的OpenCV 3 Tracking API 和Learn OpenCV's Object Tracking article 了解更多详情。

作为参考，以下是博客文章中的示例代码：

C++：

#include <opencv2/opencv.hpp>
#include <opencv2/tracking.hpp>
#include <opencv2/core/ocl.hpp>

using namespace cv;
using namespace std;

// Convert to string
#define SSTR( x ) static_cast< std::ostringstream & >( \
( std::ostringstream() << std::dec << x ) ).str()

int main(int argc, char **argv)
{
    // List of tracker types in OpenCV 3.2
    // NOTE : GOTURN implementation is buggy and does not work.
    string trackerTypes[6] = {"BOOSTING", "MIL", "KCF", "TLD","MEDIANFLOW", "GOTURN"};
    // vector <string> trackerTypes(types, std::end(types));

    // Create a tracker
    string trackerType = trackerTypes[2];

    Ptr<Tracker> tracker;

    #if (CV_MINOR_VERSION < 3)
    {
        tracker = Tracker::create(trackerType);
    }
    #else
    {
        if (trackerType == "BOOSTING")
            tracker = TrackerBoosting::create();
        if (trackerType == "MIL")
            tracker = TrackerMIL::create();
        if (trackerType == "KCF")
            tracker = TrackerKCF::create();
        if (trackerType == "TLD")
            tracker = TrackerTLD::create();
        if (trackerType == "MEDIANFLOW")
            tracker = TrackerMedianFlow::create();
        if (trackerType == "GOTURN")
            tracker = TrackerGOTURN::create();
    }
    #endif
    // Read video
    VideoCapture video("videos/chaplin.mp4");

    // Exit if video is not opened
    if(!video.isOpened())
    {
        cout << "Could not read video file" << endl;
        return 1;

    }

    // Read first frame
    Mat frame;
    bool ok = video.read(frame);

    // Define initial boundibg box
    Rect2d bbox(287, 23, 86, 320);

    // Uncomment the line below to select a different bounding box
    bbox = selectROI(frame, false);

    // Display bounding box.
    rectangle(frame, bbox, Scalar( 255, 0, 0 ), 2, 1 );
    imshow("Tracking", frame);

    tracker->init(frame, bbox);

    while(video.read(frame))
    {     
        // Start timer
        double timer = (double)getTickCount();

        // Update the tracking result
        bool ok = tracker->update(frame, bbox);

        // Calculate Frames per second (FPS)
        float fps = getTickFrequency() / ((double)getTickCount() - timer);

        if (ok)
        {
            // Tracking success : Draw the tracked object
            rectangle(frame, bbox, Scalar( 255, 0, 0 ), 2, 1 );
        }
        else
        {
            // Tracking failure detected.
            putText(frame, "Tracking failure detected", Point(100,80), FONT_HERSHEY_SIMPLEX, 0.75, Scalar(0,0,255),2);
        }

        // Display tracker type on frame
        putText(frame, trackerType + " Tracker", Point(100,20), FONT_HERSHEY_SIMPLEX, 0.75, Scalar(50,170,50),2);

        // Display FPS on frame
        putText(frame, "FPS : " + SSTR(int(fps)), Point(100,50), FONT_HERSHEY_SIMPLEX, 0.75, Scalar(50,170,50), 2);

        // Display frame.
        imshow("Tracking", frame);

        // Exit if ESC pressed.
        int k = waitKey(1);
        if(k == 27)
        {
            break;
        }

    }
}

Python：

import cv2
import sys

(major_ver, minor_ver, subminor_ver) = (cv2.__version__).split('.')

if __name__ == '__main__' :

    # Set up tracker.
    # Instead of MIL, you can also use

    tracker_types = ['BOOSTING', 'MIL','KCF', 'TLD', 'MEDIANFLOW', 'GOTURN']
    tracker_type = tracker_types[2]

    if int(minor_ver) < 3:
        tracker = cv2.Tracker_create(tracker_type)
    else:
        if tracker_type == 'BOOSTING':
            tracker = cv2.TrackerBoosting_create()
        if tracker_type == 'MIL':
            tracker = cv2.TrackerMIL_create()
        if tracker_type == 'KCF':
            tracker = cv2.TrackerKCF_create()
        if tracker_type == 'TLD':
            tracker = cv2.TrackerTLD_create()
        if tracker_type == 'MEDIANFLOW':
            tracker = cv2.TrackerMedianFlow_create()
        if tracker_type == 'GOTURN':
            tracker = cv2.TrackerGOTURN_create()

    # Read video
    video = cv2.VideoCapture("videos/chaplin.mp4")

    # Exit if video not opened.
    if not video.isOpened():
        print "Could not open video"
        sys.exit()

    # Read first frame.
    ok, frame = video.read()
    if not ok:
        print 'Cannot read video file'
        sys.exit()

    # Define an initial bounding box
    bbox = (287, 23, 86, 320)

    # Uncomment the line below to select a different bounding box
    bbox = cv2.selectROI(frame, False)

    # Initialize tracker with first frame and bounding box
    ok = tracker.init(frame, bbox)

    while True:
        # Read a new frame
        ok, frame = video.read()
        if not ok:
            break

        # Start timer
        timer = cv2.getTickCount()

        # Update tracker
        ok, bbox = tracker.update(frame)

        # Calculate Frames per second (FPS)
        fps = cv2.getTickFrequency() / (cv2.getTickCount() - timer);

        # Draw bounding box
        if ok:
            # Tracking success
            p1 = (int(bbox[0]), int(bbox[1]))
            p2 = (int(bbox[0] + bbox[2]), int(bbox[1] + bbox[3]))
            cv2.rectangle(frame, p1, p2, (255,0,0), 2, 1)
        else :
            # Tracking failure
            cv2.putText(frame, "Tracking failure detected", (100,80), cv2.FONT_HERSHEY_SIMPLEX, 0.75,(0,0,255),2)

        # Display tracker type on frame
        cv2.putText(frame, tracker_type + " Tracker", (100,20), cv2.FONT_HERSHEY_SIMPLEX, 0.75, (50,170,50),2);

        # Display FPS on frame
        cv2.putText(frame, "FPS : " + str(int(fps)), (100,50), cv2.FONT_HERSHEY_SIMPLEX, 0.75, (50,170,50), 2);

        # Display result
        cv2.imshow("Tracking", frame)

        # Exit if ESC pressed
        k = cv2.waitKey(1) & 0xff
        if k == 27 : break