normal_space.hpp

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#ifndef PCL_FILTERS_IMPL_NORMAL_SPACE_SAMPLE_H_
#define PCL_FILTERS_IMPL_NORMAL_SPACE_SAMPLE_H_
 
#include <pcl/filters/normal_space.h>
 
#include <vector>
#include <list>
 
///////////////////////////////////////////////////////////////////////////////
template<typename PointT, typename NormalT> bool
pcl::NormalSpaceSampling<PointT, NormalT>::initCompute ()
{
  if (!FilterIndices<PointT>::initCompute ())
    return false;
 
  // If sample size is 0 or if the sample size is greater then input cloud size then return entire copy of cloud
  if (sample_ >= input_->size ())
  {
    PCL_ERROR ("[NormalSpaceSampling::initCompute] Requested more samples than the input cloud size: %d vs %lu\n",
               sample_, input_->size ());
    return false;
  }
 
  rng_.seed (seed_);
  return (true);
}
 
///////////////////////////////////////////////////////////////////////////////
template<typename PointT, typename NormalT> bool 
pcl::NormalSpaceSampling<PointT, NormalT>::isEntireBinSampled (boost::dynamic_bitset<> &array,
                                                               unsigned int start_index,
                                                               unsigned int length)
{
  bool status = true;
  for (unsigned int i = start_index; i < start_index + length; i++)
  {
    status &= array.test (i);
  }
  return status;
}
 
///////////////////////////////////////////////////////////////////////////////
template<typename PointT, typename NormalT> unsigned int 
pcl::NormalSpaceSampling<PointT, NormalT>::findBin (const float *normal)
{
  const unsigned ix = static_cast<unsigned> (std::round (0.5f * (binsx_ - 1.f) * (normal[0] + 1.f)));
  const unsigned iy = static_cast<unsigned> (std::round (0.5f * (binsy_ - 1.f) * (normal[1] + 1.f)));
  const unsigned iz = static_cast<unsigned> (std::round (0.5f * (binsz_ - 1.f) * (normal[2] + 1.f)));
  return ix * (binsy_*binsz_) + iy * binsz_ + iz;
}
 
///////////////////////////////////////////////////////////////////////////////
template<typename PointT, typename NormalT> void
pcl::NormalSpaceSampling<PointT, NormalT>::applyFilter (std::vector<int> &indices)
{
  if (!initCompute ())
  {
    indices = *indices_;
    return;
  }
 
  unsigned int max_values = (std::min) (sample_, static_cast<unsigned int> (input_normals_->size ()));
  // Resize output indices to sample size
  indices.resize (max_values);
  removed_indices_->resize (max_values);
  
  // Allocate memory for the histogram of normals. Normals will then be sampled from each bin.
  unsigned int n_bins = binsx_ * binsy_ * binsz_;
  // list<int> holds the indices of points in that bin. Using list to avoid repeated resizing of vectors.
  // Helps when the point cloud is large.
  std::vector<std::list <int> > normals_hg;
  normals_hg.reserve (n_bins);
  for (unsigned int i = 0; i < n_bins; i++)
    normals_hg.emplace_back();
 
  for (const auto index : *indices_)
  {
    unsigned int bin_number = findBin ((*input_normals_)[index].normal);
    normals_hg[bin_number].push_back (index);
  }
 
 
  // Setting up random access for the list created above. Maintaining the iterators to individual elements of the list
  // in a vector. Using vector now as the size of the list is known.
  std::vector<std::vector<std::list<int>::iterator> > random_access (normals_hg.size ());
  for (std::size_t i = 0; i < normals_hg.size (); i++)
  {
    random_access.emplace_back();
    random_access[i].resize (normals_hg[i].size ());
 
    std::size_t j = 0;
    for (std::list<int>::iterator itr = normals_hg[i].begin (); itr != normals_hg[i].end (); ++itr, ++j)
      random_access[i][j] = itr;
  }
  std::vector<std::size_t> start_index (normals_hg.size ());
  start_index[0] = 0;
  std::size_t prev_index = 0;
  for (std::size_t i = 1; i < normals_hg.size (); i++)
  {
    start_index[i] = prev_index + normals_hg[i-1].size ();
    prev_index = start_index[i];
  }
 
  // Maintaining flags to check if a point is sampled
  boost::dynamic_bitset<> is_sampled_flag (input_normals_->size ());
  // Maintaining flags to check if all points in the bin are sampled
  boost::dynamic_bitset<> bin_empty_flag (normals_hg.size ());
  unsigned int i = 0;
  while (i < sample_)
  {
    // Iterating through every bin and picking one point at random, until the required number of points are sampled.
    for (std::size_t j = 0; j < normals_hg.size (); j++)
    {
      unsigned int M = static_cast<unsigned int> (normals_hg[j].size ());
      if (M == 0 || bin_empty_flag.test (j)) // bin_empty_flag(i) is set if all points in that bin are sampled..
        continue;
 
      unsigned int pos = 0;
      unsigned int random_index = 0;
      std::uniform_int_distribution<unsigned> rng_uniform_distribution (0u, M - 1u);
 
      // Picking up a sample at random from jth bin
      do
      {
        random_index = rng_uniform_distribution (rng_);
        pos = start_index[j] + random_index;
      } while (is_sampled_flag.test (pos));
 
      is_sampled_flag.flip (start_index[j] + random_index);
 
      // Checking if all points in bin j are sampled.
      if (isEntireBinSampled (is_sampled_flag, start_index[j], static_cast<unsigned int> (normals_hg[j].size ()))) 
        bin_empty_flag.flip (j);
 
      unsigned int index = *(random_access[j][random_index]);
      indices[i] = index;
      i++;
      if (i == sample_)
        break;
    }
  }
  
  // If we need to return the indices that we haven't sampled
  if (extract_removed_indices_)
  {
    std::vector<int> indices_temp = indices;
    std::sort (indices_temp.begin (), indices_temp.end ());
 
    std::vector<int> all_indices_temp = *indices_;
    std::sort (all_indices_temp.begin (), all_indices_temp.end ());
    set_difference (all_indices_temp.begin (), all_indices_temp.end (), 
                    indices_temp.begin (), indices_temp.end (), 
                    inserter (*removed_indices_, removed_indices_->begin ()));
  }
}
 
#define PCL_INSTANTIATE_NormalSpaceSampling(T,NT) template class PCL_EXPORTS pcl::NormalSpaceSampling<T,NT>;
 
#endif    // PCL_FILTERS_IMPL_NORMAL_SPACE_SAMPLE_H_