Function FindBestMatchesOneWayIndex

src/colmap/feature/sift.cc:864–911

}

size_t FindBestMatchesOneWayIndex(const Eigen::RowMajorMatrixXi& indices,
                                  const Eigen::RowMajorMatrixXf& l2_dists,
                                  const float max_ratio,
                                  const float max_distance,
                                  std::vector<int>* matches) {
  const float max_l2_dist = kSqSiftDescriptorNorm * max_distance * max_distance;

  size_t num_matches = 0;
  matches->resize(indices.rows(), -1);

  for (int d1_idx = 0; d1_idx < indices.rows(); ++d1_idx) {
    int best_d2_idx = -1;
    float best_l2_dist = std::numeric_limits<float>::max();
    float second_best_l2_dist = std::numeric_limits<float>::max();
    for (int n_idx = 0; n_idx < indices.cols(); ++n_idx) {
      const int d2_idx = indices(d1_idx, n_idx);
      const float l2_dist = l2_dists(d1_idx, n_idx);
      if (l2_dist < best_l2_dist) {
        best_d2_idx = d2_idx;
        second_best_l2_dist = best_l2_dist;
        best_l2_dist = l2_dist;
      } else if (l2_dist < second_best_l2_dist) {
        second_best_l2_dist = l2_dist;
      }
    }

    // Check if any match found.
    if (best_d2_idx == -1) {
      continue;
    }

    // Check if match distance passes threshold.
    if (best_l2_dist > max_l2_dist) {
      continue;
    }

    // Check if match passes ratio test. Keep this comparison >= in order to
    // ensure that the case of best == second_best is detected.
    if (std::sqrt(best_l2_dist) >= max_ratio * std::sqrt(second_best_l2_dist)) {
      continue;
    }

    ++num_matches;
    (*matches)[d1_idx] = best_d2_idx;
  }

  return num_matches;
}

void FindBestMatchesIndex(const Eigen::RowMajorMatrixXi& indices_1to2,
                          const Eigen::RowMajorMatrixXf& l2_dists_1to2,