std::vector<bbox_t> tracking_flow(cv::Mat new_dst_mat, bool check_error = true)
    {
        if (sync_PyrLKOpticalFlow.empty()) {
            std::cout << "sync_PyrLKOpticalFlow isn't initialized \n";
            return cur_bbox_vec;
        }

        cv::cvtColor(new_dst_mat, dst_grey, CV_BGR2GRAY, 1);

        if (src_grey.rows != dst_grey.rows || src_grey.cols != dst_grey.cols) {
            src_grey = dst_grey.clone();
            return cur_bbox_vec;
        }

        if (prev_pts_flow.cols < 1) {
            return cur_bbox_vec;
        }

        ////sync_PyrLKOpticalFlow_gpu.sparse(src_grey_gpu, dst_grey_gpu, prev_pts_flow_gpu, cur_pts_flow_gpu, status_gpu, &err_gpu);    // OpenCV 2.4.x
        sync_PyrLKOpticalFlow->calc(src_grey, dst_grey, prev_pts_flow, cur_pts_flow, status, err);    // OpenCV 3.x

        dst_grey.copyTo(src_grey);

        std::vector<bbox_t> result_bbox_vec;

        if (err.rows == cur_bbox_vec.size() && status.rows == cur_bbox_vec.size())
        {
            for (size_t i = 0; i < cur_bbox_vec.size(); ++i)
            {
                cv::Point2f cur_key_pt = cur_pts_flow.at<cv::Point2f>(0, i);
                cv::Point2f prev_key_pt = prev_pts_flow.at<cv::Point2f>(0, i);

                float moved_x = cur_key_pt.x - prev_key_pt.x;
                float moved_y = cur_key_pt.y - prev_key_pt.y;

                if (abs(moved_x) < 100 && abs(moved_y) < 100 && good_bbox_vec_flags[i])
                    if (err.at<float>(0, i) < flow_error && status.at<unsigned char>(0, i) != 0 &&
                        ((float)cur_bbox_vec[i].x + moved_x) > 0 && ((float)cur_bbox_vec[i].y + moved_y) > 0)
                    {
                        cur_bbox_vec[i].x += moved_x + 0.5;
                        cur_bbox_vec[i].y += moved_y + 0.5;
                        result_bbox_vec.push_back(cur_bbox_vec[i]);
                    }
                    else good_bbox_vec_flags[i] = false;
                else good_bbox_vec_flags[i] = false;

                //if(!check_error && !good_bbox_vec_flags[i]) result_bbox_vec.push_back(cur_bbox_vec[i]);
            }
        }

        prev_pts_flow = cur_pts_flow.clone();

        return result_bbox_vec;
    }
    std::vector<bbox_t> tracking_flow(cv::Mat dst_mat, bool check_error = true)
    {
        if (sync_PyrLKOpticalFlow_gpu.empty()) {
            std::cout << "sync_PyrLKOpticalFlow_gpu isn't initialized \n";
            return cur_bbox_vec;
        }

        int const old_gpu_id = cv::cuda::getDevice();
        if(old_gpu_id != gpu_id)
            cv::cuda::setDevice(gpu_id);

        if (dst_mat_gpu.cols == 0) {
            dst_mat_gpu = cv::cuda::GpuMat(dst_mat.size(), dst_mat.type());
            dst_grey_gpu = cv::cuda::GpuMat(dst_mat.size(), CV_8UC1);
        }

        //dst_grey_gpu.upload(dst_mat, stream);    // use BGR
        dst_mat_gpu.upload(dst_mat, stream);
        cv::cuda::cvtColor(dst_mat_gpu, dst_grey_gpu, CV_BGR2GRAY, 1, stream);

        if (src_grey_gpu.rows != dst_grey_gpu.rows || src_grey_gpu.cols != dst_grey_gpu.cols) {
            stream.waitForCompletion();
            src_grey_gpu = dst_grey_gpu.clone();
            cv::cuda::setDevice(old_gpu_id);
            return cur_bbox_vec;
        }

        ////sync_PyrLKOpticalFlow_gpu.sparse(src_grey_gpu, dst_grey_gpu, prev_pts_flow_gpu, cur_pts_flow_gpu, status_gpu, &err_gpu);    // OpenCV 2.4.x
        sync_PyrLKOpticalFlow_gpu->calc(src_grey_gpu, dst_grey_gpu, prev_pts_flow_gpu, cur_pts_flow_gpu, status_gpu, err_gpu, stream);    // OpenCV 3.x

        cv::Mat cur_pts_flow_cpu;
        cur_pts_flow_gpu.download(cur_pts_flow_cpu, stream);

        dst_grey_gpu.copyTo(src_grey_gpu, stream);

        cv::Mat err_cpu, status_cpu;
        err_gpu.download(err_cpu, stream);
        status_gpu.download(status_cpu, stream);

        stream.waitForCompletion();

        std::vector<bbox_t> result_bbox_vec;

        if (err_cpu.cols == cur_bbox_vec.size() && status_cpu.cols == cur_bbox_vec.size())
        {
            for (size_t i = 0; i < cur_bbox_vec.size(); ++i)
            {
                cv::Point2f cur_key_pt = cur_pts_flow_cpu.at<cv::Point2f>(0, i);
                cv::Point2f prev_key_pt = prev_pts_flow_cpu.at<cv::Point2f>(0, i);

                float moved_x = cur_key_pt.x - prev_key_pt.x;
                float moved_y = cur_key_pt.y - prev_key_pt.y;

                if (abs(moved_x) < 100 && abs(moved_y) < 100 && good_bbox_vec_flags[i])
                    if (err_cpu.at<float>(0, i) < flow_error && status_cpu.at<unsigned char>(0, i) != 0 &&
                        ((float)cur_bbox_vec[i].x + moved_x) > 0 && ((float)cur_bbox_vec[i].y + moved_y) > 0)
                    {
                        cur_bbox_vec[i].x += moved_x + 0.5;
                        cur_bbox_vec[i].y += moved_y + 0.5;
                        result_bbox_vec.push_back(cur_bbox_vec[i]);
                    }
                    else good_bbox_vec_flags[i] = false;
                else good_bbox_vec_flags[i] = false;

                //if(!check_error && !good_bbox_vec_flags[i]) result_bbox_vec.push_back(cur_bbox_vec[i]);
            }
        }

        cur_pts_flow_gpu.swap(prev_pts_flow_gpu);
        cur_pts_flow_cpu.copyTo(prev_pts_flow_cpu);

        if (old_gpu_id != gpu_id)
            cv::cuda::setDevice(old_gpu_id);

        return result_bbox_vec;
    }