我正在尝试使用SiftFeatureDetector，但我有未声明的标识符错误。但我导入了库：
#include <opencv2/features2d.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
// ...
SiftFeatureDetector detector; detector.detect(timg, kps, mask);
SiftDescriptorExtractor extractor;
extractor.compute(timg, kps, desc);