colmap/src/feature/utils.cc

// Copyright (c) 2022, ETH Zurich and UNC Chapel Hill.
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// Author: Johannes L. Schoenberger (jsch-at-demuc-dot-de)

#include "feature/utils.h"

#include "util/math.h"

namespace colmap {

std::vector<Eigen::Vector2d> FeatureKeypointsToPointsVector(
    const FeatureKeypoints& keypoints) {
  std::vector<Eigen::Vector2d> points(keypoints.size());
  for (size_t i = 0; i < keypoints.size(); ++i) {
    points[i] = Eigen::Vector2d(keypoints[i].x, keypoints[i].y);
  }
  return points;
}

Eigen::MatrixXf L2NormalizeFeatureDescriptors(
    const Eigen::MatrixXf& descriptors) {
  return descriptors.rowwise().normalized();
}

Eigen::MatrixXf L1RootNormalizeFeatureDescriptors(
    const Eigen::MatrixXf& descriptors) {
  Eigen::MatrixXf descriptors_normalized(descriptors.rows(),
                                         descriptors.cols());
  for (Eigen::MatrixXf::Index r = 0; r < descriptors.rows(); ++r) {
    const float norm = descriptors.row(r).lpNorm<1>();
    descriptors_normalized.row(r) = descriptors.row(r) / norm;
    descriptors_normalized.row(r) =
        descriptors_normalized.row(r).array().sqrt();
  }
  return descriptors_normalized;
}

FeatureDescriptors FeatureDescriptorsToUnsignedByte(
    const Eigen::MatrixXf& descriptors) {
  FeatureDescriptors descriptors_unsigned_byte(descriptors.rows(),
                                               descriptors.cols());
  for (Eigen::MatrixXf::Index r = 0; r < descriptors.rows(); ++r) {
    for (Eigen::MatrixXf::Index c = 0; c < descriptors.cols(); ++c) {
      const float scaled_value = std::round(512.0f * descriptors(r, c));
      descriptors_unsigned_byte(r, c) =
          TruncateCast<float, uint8_t>(scaled_value);
    }
  }
  return descriptors_unsigned_byte;
}

void ExtractTopScaleFeatures(FeatureKeypoints* keypoints,
                             FeatureDescriptors* descriptors,
                             const size_t num_features) {
  CHECK_EQ(keypoints->size(), descriptors->rows());
  CHECK_GT(num_features, 0);

  if (static_cast<size_t>(descriptors->rows()) <= num_features) {
    return;
  }

  FeatureKeypoints top_scale_keypoints;
  FeatureDescriptors top_scale_descriptors;

  std::vector<std::pair<size_t, float>> scales;
  scales.reserve(static_cast<size_t>(keypoints->size()));
  for (size_t i = 0; i < keypoints->size(); ++i) {
    scales.emplace_back(i, (*keypoints)[i].ComputeScale());
  }

  std::partial_sort(scales.begin(), scales.begin() + num_features, scales.end(),
                    [](const std::pair<size_t, float> scale1,
                       const std::pair<size_t, float> scale2) {
                      return scale1.second > scale2.second;
                    });

  top_scale_keypoints.resize(num_features);
  top_scale_descriptors.resize(num_features, descriptors->cols());
  for (size_t i = 0; i < num_features; ++i) {
    top_scale_keypoints[i] = (*keypoints)[scales[i].first];
    top_scale_descriptors.row(i) = descriptors->row(scales[i].first);
  }

  *keypoints = top_scale_keypoints;
  *descriptors = top_scale_descriptors;
}

}  // namespace colmap