random_sample.hpp

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 * $Id: extract_indices.hpp 1897 2011-07-26 20:35:49Z rusu $
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#ifndef PCL_FILTERS_IMPL_RANDOM_SAMPLE_H_
#define PCL_FILTERS_IMPL_RANDOM_SAMPLE_H_
 
#include <pcl/filters/random_sample.h>
 
 
///////////////////////////////////////////////////////////////////////////////
template<typename PointT>
void
pcl::RandomSample<PointT>::applyFilter (Indices &indices)
{
  std::size_t N = indices_->size ();  
  std::size_t sample_size = negative_ ? N - sample_ : sample_;
  // If sample size is 0 or if the sample size is greater then input cloud size
  //   then return all indices
  if (sample_size >= N)
  {
    indices = *indices_;
    removed_indices_->clear ();
  }
  else
  {
    // Resize output indices to sample size
    indices.resize (sample_size);
    if (extract_removed_indices_)
      removed_indices_->resize (N - sample_size);
 
    // Set random seed so derived indices are the same each time the filter runs
#ifdef __OpenBSD__
    srand_deterministic (seed_); // OpenBSD only offers repeatable sequences with this function
#else
    std::srand (seed_);
#endif // __OpenBSD__
 
    // Algorithm S
    std::size_t i = 0;
    std::size_t index = 0;
    std::vector<bool> added;
    if (extract_removed_indices_)
      added.resize (indices_->size (), false);
    std::size_t n = sample_size;
    while (n > 0)
    {
      // Step 1: [Generate U.] Generate a random variate U that is uniformly distributed between 0 and 1.
      const float U = unifRand ();
      // Step 2: [Test.] If N * U > n, go to Step 4. 
      if ((N * U) <= n)
      {
        // Step 3: [Select.] Select the next record in the file for the sample, and set n : = n - 1.
        if (extract_removed_indices_)
          added[index] = true;
        indices[i++] = (*indices_)[index];
        --n;
      }
      // Step 4: [Don't select.] Skip over the next record (do not include it in the sample).      
      // Set N : = N - 1.
      --N;
      ++index;
      // If n > 0, then return to Step 1; otherwise, the sample is complete and the algorithm terminates.
    }
 
    // Now populate removed_indices_ appropriately
    if (extract_removed_indices_)
    {
      std::size_t ri = 0;
      for (std::size_t i = 0; i < added.size (); i++)
      {
        if (!added[i])
        {
          (*removed_indices_)[ri++] = (*indices_)[i];
        }
      }
    }
  }
}
 
#define PCL_INSTANTIATE_RandomSample(T) template class PCL_EXPORTS pcl::RandomSample<T>;
 
#endif    // PCL_FILTERS_IMPL_RANDOM_SAMPLE_H_