从opencv3->opencv4发生改变的一些东西
https://github.com/laganiere/OpenCV3Cookbook
opencv3 -> opencv4
cv::xfeatures2d::SIFT -> cv::SIFT
cv_TM_SQDIFF -> cv::TM_SQDIFF
cv_LOAD_IMAGE_GRAYSCALE -> cv::IMREAD_GRAYSCALE
In cv::drawMatches change 2 to cv::DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS
这个按道理是完全等价的，不过在vs上会报错
add cv:: namespace for Stitcher
cv::keyPoint和descriptors之间的关系
The Keypoint is characterized by the 2D position, scale (proportional to the diameter of the neighborhood of the neighborhood that needs to be taken into account), orientation and some other parameters. The keypoint neighborhood is then analyzed by another algorithm that builds a descriptor(usually represented as a feature vector)