sample_consensus_prerejective.hpp

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#ifndef PCL_REGISTRATION_SAMPLE_CONSENSUS_PREREJECTIVE_HPP_
#define PCL_REGISTRATION_SAMPLE_CONSENSUS_PREREJECTIVE_HPP_
 
#include <pcl/search/auto.h> // for autoSelectMethod
 
namespace pcl {
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::setSourceFeatures(
    const FeatureCloudConstPtr& features)
{
  if (features == nullptr || features->empty()) {
    PCL_ERROR(
        "[pcl::%s::setSourceFeatures] Invalid or empty point cloud dataset given!\n",
        getClassName().c_str());
    return;
  }
  input_features_ = features;
}
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::setTargetFeatures(
    const FeatureCloudConstPtr& features)
{
  if (features == nullptr || features->empty()) {
    PCL_ERROR(
        "[pcl::%s::setTargetFeatures] Invalid or empty point cloud dataset given!\n",
        getClassName().c_str());
    return;
  }
  target_features_ = features;
  feature_tree_.reset(pcl::search::autoSelectMethod<FeatureT>(
      target_features_, false, pcl::search::Purpose::many_knn_search));
}
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::selectSamples(
    const PointCloudSource& cloud, int nr_samples, pcl::Indices& sample_indices)
{
  if (nr_samples > static_cast<int>(cloud.size())) {
    PCL_ERROR("[pcl::%s::selectSamples] ", getClassName().c_str());
    PCL_ERROR("The number of samples (%d) must not be greater than the number of "
              "points (%zu)!\n",
              nr_samples,
              static_cast<std::size_t>(cloud.size()));
    return;
  }
 
  sample_indices.resize(nr_samples);
  int temp_sample;
 
  // Draw random samples until n samples is reached
  for (int i = 0; i < nr_samples; i++) {
    // Select a random number
    sample_indices[i] = getRandomIndex(static_cast<int>(cloud.size()) - i);
 
    // Run through list of numbers, starting at the lowest, to avoid duplicates
    for (int j = 0; j < i; j++) {
      // Move value up if it is higher than previous selections to ensure true
      // randomness
      if (sample_indices[i] >= sample_indices[j]) {
        sample_indices[i]++;
      }
      else {
        // The new number is lower, place it at the correct point and break for a sorted
        // list
        temp_sample = sample_indices[i];
        for (int k = i; k > j; k--)
          sample_indices[k] = sample_indices[k - 1];
 
        sample_indices[j] = temp_sample;
        break;
      }
    }
  }
}
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::findSimilarFeatures(
    const pcl::Indices& sample_indices,
    std::vector<pcl::Indices>& similar_features,
    pcl::Indices& corresponding_indices)
{
  // Allocate results
  corresponding_indices.resize(sample_indices.size());
  std::vector<float> nn_distances(k_correspondences_);
 
  // Loop over the sampled features
  for (std::size_t i = 0; i < sample_indices.size(); ++i) {
    // Current feature index
    const auto& idx = sample_indices[i];
 
    // Find the k nearest feature neighbors to the sampled input feature if they are not
    // in the cache already
    if (similar_features[idx].empty())
      feature_tree_->nearestKSearch(*input_features_,
                                    idx,
                                    k_correspondences_,
                                    similar_features[idx],
                                    nn_distances);
 
    // Select one at random and add it to corresponding_indices
    if (k_correspondences_ == 1)
      corresponding_indices[i] = similar_features[idx][0];
    else
      corresponding_indices[i] =
          similar_features[idx][getRandomIndex(k_correspondences_)];
  }
}
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::computeTransformation(
    PointCloudSource& output, const Eigen::Matrix4f& guess)
{
  // Some sanity checks first
  if (!input_features_) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR(
        "No source features were given! Call setSourceFeatures before aligning.\n");
    return;
  }
  if (!target_features_) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR(
        "No target features were given! Call setTargetFeatures before aligning.\n");
    return;
  }
 
  if (input_->size() != input_features_->size()) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR("The source points and source feature points need to be in a one-to-one "
              "relationship! Current input cloud sizes: %ld vs %ld.\n",
              input_->size(),
              input_features_->size());
    return;
  }
 
  if (target_->size() != target_features_->size()) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR("The target points and target feature points need to be in a one-to-one "
              "relationship! Current input cloud sizes: %ld vs %ld.\n",
              target_->size(),
              target_features_->size());
    return;
  }
 
  if (inlier_fraction_ < 0.0f || inlier_fraction_ > 1.0f) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR("Illegal inlier fraction %f, must be in [0,1]!\n", inlier_fraction_);
    return;
  }
 
  const float similarity_threshold =
      correspondence_rejector_poly_->getSimilarityThreshold();
  if (similarity_threshold < 0.0f || similarity_threshold >= 1.0f) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR("Illegal prerejection similarity threshold %f, must be in [0,1[!\n",
              similarity_threshold);
    return;
  }
 
  if (k_correspondences_ <= 0) {
    PCL_ERROR("[pcl::%s::computeTransformation] ", getClassName().c_str());
    PCL_ERROR("Illegal correspondence randomness %d, must be > 0!\n",
              k_correspondences_);
    return;
  }
 
  // Initialize prerejector (similarity threshold already set to default value in
  // constructor)
  correspondence_rejector_poly_->setInputSource(input_);
  correspondence_rejector_poly_->setInputTarget(target_);
  correspondence_rejector_poly_->setCardinality(nr_samples_);
  int num_rejections = 0; // For debugging
 
  // Initialize results
  final_transformation_ = guess;
  inliers_.clear();
  float lowest_error = std::numeric_limits<float>::max();
  converged_ = false;
 
  // Temporaries
  pcl::Indices inliers;
  float inlier_fraction;
  float error;
 
  // If guess is not the Identity matrix we check it
  if (!guess.isApprox(Eigen::Matrix4f::Identity(), 0.01f)) {
    getFitness(inliers, error);
    inlier_fraction =
        static_cast<float>(inliers.size()) / static_cast<float>(input_->size());
 
    if (inlier_fraction >= inlier_fraction_ && error < lowest_error) {
      inliers_ = inliers;
      lowest_error = error;
      converged_ = true;
    }
  }
 
  // Feature correspondence cache
  std::vector<pcl::Indices> similar_features(input_->size());
 
  // Start
  for (int i = 0; i < max_iterations_; ++i) {
    // Temporary containers
    pcl::Indices sample_indices;
    pcl::Indices corresponding_indices;
 
    // Draw nr_samples_ random samples
    selectSamples(*input_, nr_samples_, sample_indices);
 
    // Find corresponding features in the target cloud
    findSimilarFeatures(sample_indices, similar_features, corresponding_indices);
 
    // Apply prerejection
    if (!correspondence_rejector_poly_->thresholdPolygon(sample_indices,
                                                         corresponding_indices)) {
      ++num_rejections;
      continue;
    }
 
    // Estimate the transform from the correspondences, write to transformation_
    transformation_estimation_->estimateRigidTransformation(
        *input_, sample_indices, *target_, corresponding_indices, transformation_);
 
    // Take a backup of previous result
    const Matrix4 final_transformation_prev = final_transformation_;
 
    // Set final result to current transformation
    final_transformation_ = transformation_;
 
    // Transform the input and compute the error (uses input_ and final_transformation_)
    getFitness(inliers, error);
 
    // Restore previous result
    final_transformation_ = final_transformation_prev;
 
    // If the new fit is better, update results
    inlier_fraction =
        static_cast<float>(inliers.size()) / static_cast<float>(input_->size());
 
    // Update result if pose hypothesis is better
    if (inlier_fraction >= inlier_fraction_ && error < lowest_error) {
      inliers_ = inliers;
      lowest_error = error;
      converged_ = true;
      final_transformation_ = transformation_;
    }
  }
 
  // Apply the final transformation
  if (converged_)
    transformPointCloud(*input_, output, final_transformation_);
 
  // Debug output
  PCL_DEBUG("[pcl::%s::computeTransformation] Rejected %i out of %i generated pose "
            "hypotheses.\n",
            getClassName().c_str(),
            num_rejections,
            max_iterations_);
}
 
template <typename PointSource, typename PointTarget, typename FeatureT>
void
SampleConsensusPrerejective<PointSource, PointTarget, FeatureT>::getFitness(
    pcl::Indices& inliers, float& fitness_score)
{
  // Initialize variables
  inliers.clear();
  inliers.reserve(input_->size());
  fitness_score = 0.0f;
 
  // Use squared distance for comparison with NN search results
  const float max_range = corr_dist_threshold_ * corr_dist_threshold_;
 
  // Transform the input dataset using the final transformation
  PointCloudSource input_transformed;
  input_transformed.resize(input_->size());
  transformPointCloud(*input_, input_transformed, final_transformation_);
 
  // For each point in the source dataset
  for (std::size_t i = 0; i < input_transformed.size(); ++i) {
    // Find its nearest neighbor in the target
    pcl::Indices nn_indices(1);
    std::vector<float> nn_dists(1);
    tree_->nearestKSearch(input_transformed[i], 1, nn_indices, nn_dists);
 
    // Check if point is an inlier
    if (nn_dists[0] < max_range) {
      // Update inliers
      inliers.push_back(i);
 
      // Update fitness score
      fitness_score += nn_dists[0];
    }
  }
 
  // Calculate MSE
  if (!inliers.empty())
    fitness_score /= static_cast<float>(inliers.size());
  else
    fitness_score = std::numeric_limits<float>::max();
}
 
} // namespace pcl
 
#endif