如何使用基于Flann的匹配器进行精确匹配？如果未找到匹配项，则应将输出显示为No Match Found

Question

1. 如何使用基于Flann的匹配器进行精确匹配？
2. 如果未找到匹配项，则应将输出设为“未找到匹配项”。
3. 也可以显示准确度百分比。

以下是正在进行匹配的代码：

// Match 
  vector<vector<DMatch> > knnMatches;
    Mat testDesc;
    int knn = 1;
    vector<int> bestMatches;
    FeatureDetector *detector = new SurfFeatureDetector();
    DescriptorExtractor *extractor = new SurfDescriptorExtractor();
    DescriptorMatcher *matcher = new FlannBasedMatcher();  // ANN

        trainDesc.push_back(desc);    
        trainImgs.push_back(img_name);
        int temp = 0;
        bestMatches.push_back(temp);        

      matcher->knnMatch(testDesc, knnMatches, knn);

      // Filter results
      for (vector<vector<DMatch> >::const_iterator it = knnMatches.begin();
           it != knnMatches.end(); ++it) {
        for (vector<DMatch>::const_iterator it2 = it->begin(); it2 != it->end();
             ++it2) {
          ++bestMatches[(*it2).imgIdx];
        }
      }

      // Find best match
      int bestScore = 0;
      int bestIdx = -1;
      for (int i = 0; i < bestMatches.size(); ++i) {
        if (bestMatches[i] >= bestScore) {
          bestScore = bestMatches[i];
          cout << "best Score inside if  is:" << bestScore << endl;
           cout << "best Matches inside if  is:" << bestMatches[i] << endl;
          bestIdx = i;
        }
      }

      if (debug > 0)
        cout << "Best match: " << trainImgs[bestIdx] << " Score: " << bestScore
             << "bestidx: " << bestIdx << endl;
      cout << trainImgs[bestIdx] << endl;