External features extraction

theia_opencv

/* Reimplementation of `AddImagesToReconstructionBuilder`
   https://github.com/sweeneychris/TheiaSfM/blob/master/applications/build_reconstruction.cc#L334
   Using an external local features extractor. In this case AKAZE from OpenCV.
*/
void AddImagesToReconstructionBuilder(
    ReconstructionBuilder* reconstruction_builder) {
  std::vector<std::string> image_files;
  CHECK(theia::GetFilepathsFromWildcard(FLAGS_images, &image_files));

  // Create the feature matcher.
  theia::FeatureMatcherOptions matching_options;
  theia::VerifyTwoViewMatchesOptions verification_options;
  SetMatchingOptions(&matching_options, &verification_options);
  const theia::MatchingStrategy matching_strategy =
      StringToMatchingStrategyType(FLAGS_matching_strategy);
  std::unique_ptr<theia::FeatureMatcher<theia::L2> > matcher =
      CreateFeatureMatcher(matching_strategy, matching_options);

  cv::Mat img, opencv_descs;
  std::vector<cv::KeyPoint> opencv_kpts;
  cv::Ptr<cv::Feature2D> extractor = cv::AKAZE::create();

  std::vector<theia::Keypoint> theia_kpts;
  std::vector<Eigen::VectorXf> theia_descs;

  for (size_t i = 0; i < image_files.size(); ++i) {
    img = cv::imread(image_files[i], cv::IMREAD_COLOR);
    extractor->detectAndCompute(img, cv::Mat(), opencv_kpts, opencv_descs);

    // conversion between OpenCV/Theia
    opencv_kpts_to_theia(opencv_kpts, &theia_kpts);
    opencv_descriptors_to_theia(opencv_descs, &theia_descs);

    std::string image_name;
    theia::GetFilenameFromFilepath(image_files[i], true, &image_name);

    matcher->AddImage(image_name, theia_kpts, theia_descs);
    LOG(INFO) << "Added Image " << image_name << " with "
              << theia_kpts.size() << " Keypoints, "
              << theia_descs.size() << " Descriptors";
  }

  LOG(INFO) << "Perform MATCHING!";

  std::vector<theia::ImagePairMatch> image_matches;
  //matcher->MatchImages(&image_matches);

  // Or, with geometric verification:
  matcher->MatchImagesWithGeometricVerification(
    verification_options, &image_matches);

  // Optionally read the intrinsics from a calibration file.
  std::vector<theia::CameraIntrinsicsPrior> camera_intrinsics_prior;
  ReadIntrinsicsFromCalibrationFile(image_files, &camera_intrinsics_prior);

  // Write the matches out.
  LOG(INFO) << "Writing matches to file: " << FLAGS_output_matches_file;
  CHECK(theia::WriteMatchesAndGeometry(FLAGS_output_matches_file,
                                       image_files,
                                       camera_intrinsics_prior, image_matches))
      << "Could not write the matches to " << FLAGS_output_matches_file;

  // Add all the views.
  for (int i = 0; i < image_files.size(); i++) {
    reconstruction_builder->AddImage(image_files[i]);
  }

  // Add the matches.
  for (const auto& match : image_matches) {
    CHECK(reconstruction_builder->AddTwoViewMatch(match.image1,
                                                  match.image2,
                                                  match));
  }
}

edgarriba,

Would you mind to share your code for the following functions?
opencv_kpts_to_theia(opencv_kpts, &theia_kpts);
opencv_descriptors_to_theia(opencv_descs, &theia_descs);
I need to use these functions but don't want to reinvent the wheels.... Thank you!