《PCL点云库学习&VS2010(X64)》Part 35 VFH_Recognition——FLANN_Build_Tree

#include <pcl/point_types.h>
#include <pcl/point_cloud.h>
#include <pcl/console/parse.h>
#include <pcl/console/print.h>
#include <pcl/io/pcd_io.h>
#include <boost/filesystem.hpp>
#include <flann/flann.h>
#include <flann/io/hdf5.h>
#include <fstream>

typedef std::pair<std::string, std::vector<float> > vfh_model;

/** \brief Loads an n-D histogram file as a VFH signature
  * \param path the input file name
  * \param vfh the resultant VFH model
  */
bool
loadHist (const boost::filesystem::path &path, vfh_model &vfh)
{
  int vfh_idx;
  // Load the file as a PCD
  try
  {
    pcl::PCLPointCloud2 cloud;
    int version;
    Eigen::Vector4f origin;
    Eigen::Quaternionf orientation;
    pcl::PCDReader r;
    int type; unsigned int idx;
    r.readHeader (path.string (), cloud, origin, orientation, version, type, idx);

    vfh_idx = pcl::getFieldIndex (cloud, "vfh");
    if (vfh_idx == -1)
      return (false);
    if ((int)cloud.width * cloud.height != 1)
      return (false);
  }
  catch (const pcl::InvalidConversionException&)
  {
    return (false);
  }

  // Treat the VFH signature as a single Point Cloud
  pcl::PointCloud <pcl::VFHSignature308> point;
  pcl::io::loadPCDFile (path.string (), point);
  vfh.second.resize (308);

  std::vector <pcl::PCLPointField> fields;
  pcl::getFieldIndex (point, "vfh", fields);

  for (size_t i = 0; i < fields[vfh_idx].count; ++i)
  {
    vfh.second[i] = point.points[0].histogram[i];
  }
  vfh.first = path.string ();
  return (true);
}

/** \brief Load a set of VFH features that will act as the model (training data)
  * \param argc the number of arguments (pass from main ())
  * \param argv the actual command line arguments (pass from main ())
  * \param extension the file extension containing the VFH features
  * \param models the resultant vector of histogram models
  */
void
loadFeatureModels (const boost::filesystem::path &base_dir, const std::string &extension, 
                   std::vector<vfh_model> &models)
{
  if (!boost::filesystem::exists (base_dir) && !boost::filesystem::is_directory (base_dir))
    return;

  for (boost::filesystem::directory_iterator it (base_dir); it != boost::filesystem::directory_iterator (); ++it)
  {
    if (boost::filesystem::is_directory (it->status ()))
    {
      std::stringstream ss;
      ss << it->path ();
      pcl::console::print_highlight ("Loading %s (%lu models loaded so far).\n", ss.str ().c_str (), (unsigned long)models.size ());
      loadFeatureModels (it->path (), extension, models);
    }
    if (boost::filesystem::is_regular_file (it->status ()) && boost::filesystem::extension (it->path ()) == extension)
    {
      vfh_model m;
      if (loadHist (base_dir / it->path ().filename (), m))
        models.push_back (m);
    }
  }
}

int
main (int argc, char** argv)
{
  if (argc < 2)
  {
    PCL_ERROR ("Need at least two parameters! Syntax is: %s [model_directory] [options]\n", argv[0]);
    return (-1);
  }

  std::string extension (".pcd");
  transform (extension.begin (), extension.end (), extension.begin (), (int(*)(int))tolower);

  std::string kdtree_idx_file_name = "kdtree.idx";
  std::string training_data_h5_file_name = "training_data.h5";
  std::string training_data_list_file_name = "training_data.list";

  std::vector<vfh_model> models;

  // Load the model histograms
  loadFeatureModels (argv[1], extension, models);
  pcl::console::print_highlight ("Loaded %d VFH models. Creating training data %s/%s.\n", 
      (int)models.size (), training_data_h5_file_name.c_str (), training_data_list_file_name.c_str ());

  // Convert data into FLANN format
  flann::Matrix<float> data (new float[models.size () * models[0].second.size ()], models.size (), models[0].second.size ());

  for (size_t i = 0; i < data.rows; ++i)
    for (size_t j = 0; j < data.cols; ++j)
      data[i][j] = models[i].second[j];

  // Save data to disk (list of models)
  flann::save_to_file (data, training_data_h5_file_name, "training_data");
  std::ofstream fs;
  fs.open (training_data_list_file_name.c_str ());
  for (size_t i = 0; i < models.size (); ++i)
    fs << models[i].first << "\n";
  fs.close ();
 
  // Build the tree index and save it to disk
  pcl::console::print_error ("Building the kdtree index (%s) for %d elements...\n", kdtree_idx_file_name.c_str (), (int)data.rows);
  flann::Index<flann::ChiSquareDistance<float> > index (data, flann::LinearIndexParams ());
  //flann::Index<flann::ChiSquareDistance<float> > index (data, flann::KDTreeIndexParams (4));
  index.buildIndex ();
  index.save (kdtree_idx_file_name);
  delete[] data.ptr ();

  return (0);
}
总结：
1、注意将数据转换为FLANN的存储格式，实际上是将model中的数据重新分配给data[i][j]；
2、ChiSquareDistance为卡方距离；
3、此处建立的是卡方距离索引，index.buildIndex();
4、FLANN的数据在最后需要析构，delete[] data.ptr()。
来源：oschina
链接：https://my.oschina.net/u/4324861/blog/4266747
标签
flann