c++ - OpenCV goodFeaturesToTrack's status are zeros -

trying implement optical flow ios opencv 3.1 .

i built basic stuff shown in below code , features points goodfeaturestotrack thing no point being tracked, , status results zeros (not tracked).

cv::mat gray;         // current gray-level image cv::mat gray_prev;  std::vector<cv::point2f> features;  // detected features std::vector<cv::point2f> newfeatures;  std::vector<uchar> status; // status of tracked features std::vector<float> err;    // error in tracking cv::termcriteria _termcrit = cv::termcriteria(cv::termcriteria::count|cv::termcriteria::eps,20,0.03);   -(void)processimage:(cv::mat&)image {      //-------------------- optical flow ---------------------      cv::cvtcolor(image, gray, cv_bgr2gray);      if(gray_prev.empty()) {         gray.copyto(gray_prev);     }      cv::goodfeaturestotrack(gray, features, 20, 0.01, 10);     cv::calcopticalflowpyrlk(gray_prev, gray, features, newfeatures, status, err,  cv::size(10, 10), 3, _termcrit, 0, 0.001);      // draw circles features points     (int = 0; < features.size(); i++) {         circle(image, features[i], 10, cv::scalar(250,250,250));     }      (int y = 0; y < status.size(); y++) {         nslog(@"status: %d", status[y]); // 0     }      std::swap(newfeatures, features);     cv::swap(gray_prev, gray); } 

you should call

cv::goodfeaturestotrack(gray, features, 20, 0.01, 10); 

only first initialisation of features list, , not on every cycle. doing reseting features list match current frame on every cycle there no displacement in features.

also, if want displacement between 2 frames should call

cv::goodfeaturestotrack(**gray_prev**, features ....