PCA-SIFT算法的实现，PCA-SIFT是对SIFT算法的改进，用PCA替代SIFT算法中的第四步，提高了效率，且准确率更高-PCA-SIFT algorithm implementation, PCA-SIFT SIFT algorithm is an improved SIFT algorithm with PCA instead of the fourth step, improve efficiency, and highe