#include <opencv2/opencv.hpp>
#include <opencv2/features2d.hpp>
// initialize detector
cv::Ptr<cv::FeatureDetector> detector = cv::ORB::create();
// detect features and descriptor
std::vector<cv::KeyPoint> keypoints1;
cv::Mat descriptors1;
detector->detectAndCompute( test_im_gray, cv::Mat(), keypoints1, descriptors1 );