voxel_grid.h

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#pragma once
 
#include <pcl/filters/filter.h>
#include <limits>
 
namespace pcl
{
  /** \brief Obtain the maximum and minimum points in 3D from a given point cloud.
      * \param[in] cloud the pointer to a pcl::PCLPointCloud2 dataset
      * \param[in] x_idx the index of the X channel
      * \param[in] y_idx the index of the Y channel
      * \param[in] z_idx the index of the Z channel
      * \param[out] min_pt the minimum data point
      * \param[out] max_pt the maximum data point
   */
  PCL_EXPORTS void
  getMinMax3D (const pcl::PCLPointCloud2ConstPtr &cloud, int x_idx, int y_idx, int z_idx,
              Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt);
 
  /** \brief Obtain the maximum and minimum points in 3D from a given point cloud.
    * \param[in] cloud the pointer to a pcl::PCLPointCloud2 dataset
    * \param[in] indices the point cloud indices that need to be considered
    * \param[in] x_idx the index of the X channel
    * \param[in] y_idx the index of the Y channel
    * \param[in] z_idx the index of the Z channel
    * \param[out] min_pt the minimum data point
    * \param[out] max_pt the maximum data point
   */
  PCL_EXPORTS void
  getMinMax3D (const pcl::PCLPointCloud2ConstPtr &cloud, const Indices &indices, int x_idx, int y_idx, int z_idx,
              Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt);
 
  /** \brief Obtain the maximum and minimum points in 3D from a given point cloud.
    * \note Performs internal data filtering as well.
    * \param[in] cloud the pointer to a pcl::PCLPointCloud2 dataset
    * \param[in] x_idx the index of the X channel
    * \param[in] y_idx the index of the Y channel
    * \param[in] z_idx the index of the Z channel
    * \param[in] distance_field_name the name of the dimension to filter data along to
    * \param[in] min_distance the minimum acceptable value in \a distance_field_name data
    * \param[in] max_distance the maximum acceptable value in \a distance_field_name data
    * \param[out] min_pt the minimum data point
    * \param[out] max_pt the maximum data point
    * \param[in] limit_negative \b false if data \b inside of the [min_distance; max_distance] interval should be
    * considered, \b true otherwise.
   */
  PCL_EXPORTS void
  getMinMax3D (const pcl::PCLPointCloud2ConstPtr &cloud, int x_idx, int y_idx, int z_idx,
              const std::string &distance_field_name, float min_distance, float max_distance,
              Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt, bool limit_negative = false);
 
  /** \brief Obtain the maximum and minimum points in 3D from a given point cloud.
    * \note Performs internal data filtering as well.
    * \param[in] cloud the pointer to a pcl::PCLPointCloud2 dataset
    * \param[in] indices the point cloud indices that need to be considered
    * \param[in] x_idx the index of the X channel
    * \param[in] y_idx the index of the Y channel
    * \param[in] z_idx the index of the Z channel
    * \param[in] distance_field_name the name of the dimension to filter data along to
    * \param[in] min_distance the minimum acceptable value in \a distance_field_name data
    * \param[in] max_distance the maximum acceptable value in \a distance_field_name data
    * \param[out] min_pt the minimum data point
    * \param[out] max_pt the maximum data point
    * \param[in] limit_negative \b false if data \b inside of the [min_distance; max_distance] interval should be
    * considered, \b true otherwise.
   */
  PCL_EXPORTS void
  getMinMax3D (const pcl::PCLPointCloud2ConstPtr &cloud, const Indices &indices, int x_idx, int y_idx, int z_idx,
               const std::string &distance_field_name, float min_distance, float max_distance,
               Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt, bool limit_negative = false);
 
  /** \brief Get the relative cell indices of the "upper half" 13 neighbors.
    * \note Useful in combination with getNeighborCentroidIndices() from \ref VoxelGrid
    * \ingroup filters
    */
  inline Eigen::MatrixXi
  getHalfNeighborCellIndices ()
  {
    Eigen::MatrixXi relative_coordinates (3, 13);
    int idx = 0;
 
    // 0 - 8
    for (int i = -1; i < 2; i++)
    {
      for (int j = -1; j < 2; j++)
      {
        relative_coordinates (0, idx) = i;
        relative_coordinates (1, idx) = j;
        relative_coordinates (2, idx) = -1;
        idx++;
      }
    }
    // 9 - 11
    for (int i = -1; i < 2; i++)
    {
      relative_coordinates (0, idx) = i;
      relative_coordinates (1, idx) = -1;
      relative_coordinates (2, idx) = 0;
      idx++;
    }
    // 12
    relative_coordinates (0, idx) = -1;
    relative_coordinates (1, idx) = 0;
    relative_coordinates (2, idx) = 0;
 
    return (relative_coordinates);
  }
 
  /** \brief Get the relative cell indices of all the 26 neighbors.
    * \note Useful in combination with getNeighborCentroidIndices() from \ref VoxelGrid
    * \ingroup filters
    */
  inline Eigen::MatrixXi
  getAllNeighborCellIndices ()
  {
    Eigen::MatrixXi relative_coordinates = getHalfNeighborCellIndices ();
    Eigen::MatrixXi relative_coordinates_all( 3, 26);
    relative_coordinates_all.block<3, 13> (0, 0) = relative_coordinates;
    relative_coordinates_all.block<3, 13> (0, 13) = -relative_coordinates;
    return (relative_coordinates_all);
  }
 
  /** \brief Get the minimum and maximum values on each of the 3 (x-y-z) dimensions
    * in a given pointcloud, without considering points outside of a distance threshold from the laser origin
    * \param[in] cloud the point cloud data message
    * \param[in] distance_field_name the field name that contains the distance values
    * \param[in] min_distance the minimum distance a point will be considered from
    * \param[in] max_distance the maximum distance a point will be considered to
    * \param[out] min_pt the resultant minimum bounds
    * \param[out] max_pt the resultant maximum bounds
    * \param[in] limit_negative if set to true, then all points outside of the interval (min_distance;max_distace) are considered
    * \ingroup filters
    */
  template <typename PointT> void
  getMinMax3D (const typename pcl::PointCloud<PointT>::ConstPtr &cloud,
               const std::string &distance_field_name, float min_distance, float max_distance,
               Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt, bool limit_negative = false);
 
  /** \brief Get the minimum and maximum values on each of the 3 (x-y-z) dimensions
    * in a given pointcloud, without considering points outside of a distance threshold from the laser origin
    * \param[in] cloud the point cloud data message
    * \param[in] indices the vector of indices to use
    * \param[in] distance_field_name the field name that contains the distance values
    * \param[in] min_distance the minimum distance a point will be considered from
    * \param[in] max_distance the maximum distance a point will be considered to
    * \param[out] min_pt the resultant minimum bounds
    * \param[out] max_pt the resultant maximum bounds
    * \param[in] limit_negative if set to true, then all points outside of the interval (min_distance;max_distace) are considered
    * \ingroup filters
    */
  template <typename PointT> void
  getMinMax3D (const typename pcl::PointCloud<PointT>::ConstPtr &cloud,
               const Indices &indices,
               const std::string &distance_field_name, float min_distance, float max_distance,
               Eigen::Vector4f &min_pt, Eigen::Vector4f &max_pt, bool limit_negative = false);
 
  /** \brief VoxelGrid assembles a local 3D grid over a given PointCloud, and downsamples + filters the data.
    *
    * The VoxelGrid class creates a *3D voxel grid* (think about a voxel
    * grid as a set of tiny 3D boxes in space) over the input point cloud data.
    * Then, in each *voxel* (i.e., 3D box), all the points present will be
    * approximated (i.e., *downsampled*) with their centroid. This approach is
    * a bit slower than approximating them with the center of the voxel, but it
    * represents the underlying surface more accurately.
    *
    * \author Radu B. Rusu, Bastian Steder
    * \ingroup filters
    */
  template <typename PointT>
  class VoxelGrid: public Filter<PointT>
  {
    protected:
      using Filter<PointT>::filter_name_;
      using Filter<PointT>::getClassName;
      using Filter<PointT>::input_;
      using Filter<PointT>::indices_;
 
      using PointCloud = typename Filter<PointT>::PointCloud;
      using PointCloudPtr = typename PointCloud::Ptr;
      using PointCloudConstPtr = typename PointCloud::ConstPtr;
 
    public:
 
      using Ptr = shared_ptr<VoxelGrid<PointT> >;
      using ConstPtr = shared_ptr<const VoxelGrid<PointT> >;
 
      PCL_MAKE_ALIGNED_OPERATOR_NEW
 
      /** \brief Empty constructor. */
      VoxelGrid () :
        leaf_size_ (Eigen::Vector4f::Zero ()),
        inverse_leaf_size_ (Eigen::Array4f::Zero ()),
        min_b_ (Eigen::Vector4i::Zero ()),
        max_b_ (Eigen::Vector4i::Zero ()),
        div_b_ (Eigen::Vector4i::Zero ()),
        divb_mul_ (Eigen::Vector4i::Zero ())
      {
        filter_name_ = "VoxelGrid";
      }
 
      /** \brief Destructor. */
      ~VoxelGrid () override = default;
 
      /** \brief Set the voxel grid leaf size.
        * \param[in] leaf_size the voxel grid leaf size
        */
      inline void
      setLeafSize (const Eigen::Vector4f &leaf_size)
      {
        leaf_size_ = leaf_size;
        // Avoid division errors
        if (leaf_size_[3] == 0)
          leaf_size_[3] = 1;
        // Use multiplications instead of divisions
        inverse_leaf_size_ = Eigen::Array4f::Ones () / leaf_size_.array ();
      }
 
      /** \brief Set the voxel grid leaf size.
        * \param[in] lx the leaf size for X
        * \param[in] ly the leaf size for Y
        * \param[in] lz the leaf size for Z
        */
      inline void
      setLeafSize (float lx, float ly, float lz)
      {
        leaf_size_[0] = lx; leaf_size_[1] = ly; leaf_size_[2] = lz;
        // Avoid division errors
        if (leaf_size_[3] == 0)
          leaf_size_[3] = 1;
        // Use multiplications instead of divisions
        inverse_leaf_size_ = Eigen::Array4f::Ones () / leaf_size_.array ();
      }
 
      /** \brief Get the voxel grid leaf size. */
      inline Eigen::Vector3f
      getLeafSize () const { return (leaf_size_.head<3> ()); }
 
      /** \brief Set to true if all fields need to be downsampled, or false if just XYZ.
        * \param[in] downsample the new value (true/false)
        */
      inline void
      setDownsampleAllData (bool downsample) { downsample_all_data_ = downsample; }
 
      /** \brief Get the state of the internal downsampling parameter (true if
        * all fields need to be downsampled, false if just XYZ).
        */
      inline bool
      getDownsampleAllData () const { return (downsample_all_data_); }
 
      /** \brief Set the minimum number of points required for a voxel to be used.
        * \param[in] min_points_per_voxel the minimum number of points for required for a voxel to be used
        */
      inline void
      setMinimumPointsNumberPerVoxel (unsigned int min_points_per_voxel) { min_points_per_voxel_ = min_points_per_voxel; }
 
      /** \brief Return the minimum number of points required for a voxel to be used.
       */
      inline unsigned int
      getMinimumPointsNumberPerVoxel () const { return min_points_per_voxel_; }
 
      /** \brief Set to true if leaf layout information needs to be saved for later access.
        * \param[in] save_leaf_layout the new value (true/false)
        */
      inline void
      setSaveLeafLayout (bool save_leaf_layout) { save_leaf_layout_ = save_leaf_layout; }
 
      /** \brief Returns true if leaf layout information will to be saved for later access. */
      inline bool
      getSaveLeafLayout () const { return (save_leaf_layout_); }
 
      /** \brief Get the minimum coordinates of the bounding box (after
        * filtering is performed).
        */
      inline Eigen::Vector3i
      getMinBoxCoordinates () const { return (min_b_.head<3> ()); }
 
      /** \brief Get the minimum coordinates of the bounding box (after
        * filtering is performed).
        */
      inline Eigen::Vector3i
      getMaxBoxCoordinates () const { return (max_b_.head<3> ()); }
 
      /** \brief Get the number of divisions along all 3 axes (after filtering
        * is performed).
        */
      inline Eigen::Vector3i
      getNrDivisions () const { return (div_b_.head<3> ()); }
 
      /** \brief Get the multipliers to be applied to the grid coordinates in
        * order to find the centroid index (after filtering is performed).
        */
      inline Eigen::Vector3i
      getDivisionMultiplier () const { return (divb_mul_.head<3> ()); }
 
      /** \brief Returns the index in the resulting downsampled cloud of the specified point.
        *
        * \note for efficiency, user must make sure that the saving of the leaf layout is enabled and filtering
        * performed, and that the point is inside the grid, to avoid invalid access (or use
        * getGridCoordinates+getCentroidIndexAt)
        *
        * \param[in] p the point to get the index at
        */
      inline int
      getCentroidIndex (const PointT &p) const
      {
        return (leaf_layout_.at ((Eigen::Vector4i (static_cast<int> (std::floor (p.x * inverse_leaf_size_[0])),
                                                   static_cast<int> (std::floor (p.y * inverse_leaf_size_[1])),
                                                   static_cast<int> (std::floor (p.z * inverse_leaf_size_[2])), 0) - min_b_).dot (divb_mul_)));
      }
 
      /** \brief Returns the indices in the resulting downsampled cloud of the points at the specified grid coordinates,
        * relative to the grid coordinates of the specified point (or -1 if the cell was empty/out of bounds).
        * \param[in] reference_point the coordinates of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[in] relative_coordinates matrix with the columns being the coordinates of the requested cells, relative to the reference point's cell
        * \note for efficiency, user must make sure that the saving of the leaf layout is enabled and filtering performed
        */
      inline std::vector<int>
      getNeighborCentroidIndices (const PointT &reference_point, const Eigen::MatrixXi &relative_coordinates) const
      {
        Eigen::Vector4i ijk (static_cast<int> (std::floor (reference_point.x * inverse_leaf_size_[0])),
                             static_cast<int> (std::floor (reference_point.y * inverse_leaf_size_[1])),
                             static_cast<int> (std::floor (reference_point.z * inverse_leaf_size_[2])), 0);
        Eigen::Array4i diff2min = min_b_ - ijk;
        Eigen::Array4i diff2max = max_b_ - ijk;
        std::vector<int> neighbors (relative_coordinates.cols());
        for (Eigen::Index ni = 0; ni < relative_coordinates.cols (); ni++)
        {
          Eigen::Vector4i displacement = (Eigen::Vector4i() << relative_coordinates.col(ni), 0).finished();
          // checking if the specified cell is in the grid
          if ((diff2min <= displacement.array()).all() && (diff2max >= displacement.array()).all())
            neighbors[ni] = leaf_layout_[((ijk + displacement - min_b_).dot (divb_mul_))]; // .at() can be omitted
          else
            neighbors[ni] = -1; // cell is out of bounds, consider it empty
        }
        return (neighbors);
      }
 
      /** \brief Returns the layout of the leafs for fast access to cells relative to current position.
        * \note position at (i-min_x) + (j-min_y)*div_x + (k-min_z)*div_x*div_y holds the index of the element at coordinates (i,j,k) in the grid (-1 if empty)
        */
      inline std::vector<int>
      getLeafLayout () const { return (leaf_layout_); }
 
      /** \brief Returns the corresponding (i,j,k) coordinates in the grid of point (x,y,z).
        * \param[in] x the X point coordinate to get the (i, j, k) index at
        * \param[in] y the Y point coordinate to get the (i, j, k) index at
        * \param[in] z the Z point coordinate to get the (i, j, k) index at
        */
      inline Eigen::Vector3i
      getGridCoordinates (float x, float y, float z) const
      {
        return {static_cast<int> (std::floor (x * inverse_leaf_size_[0])),
                                 static_cast<int> (std::floor (y * inverse_leaf_size_[1])),
                                 static_cast<int> (std::floor (z * inverse_leaf_size_[2]))};
      }
 
      /** \brief Returns the index in the downsampled cloud corresponding to a given set of coordinates.
        * \param[in] ijk the coordinates (i,j,k) in the grid (-1 if empty)
        */
      inline int
      getCentroidIndexAt (const Eigen::Vector3i &ijk) const
      {
        int idx = ((Eigen::Vector4i() << ijk, 0).finished() - min_b_).dot (divb_mul_);
        if (idx < 0 || idx >= static_cast<int> (leaf_layout_.size ())) // this checks also if leaf_layout_.size () == 0 i.e. everything was computed as needed
        {
          //if (verbose)
          //  PCL_ERROR ("[pcl::%s::getCentroidIndexAt] Specified coordinate is outside grid bounds, or leaf layout is not saved, make sure to call setSaveLeafLayout(true) and filter(output) first!\n", getClassName ().c_str ());
          return (-1);
        }
        return (leaf_layout_[idx]);
      }
 
      /** \brief Provide the name of the field to be used for filtering data. In conjunction with  \a setFilterLimits,
        * points having values outside this interval will be discarded.
        * \param[in] field_name the name of the field that contains values used for filtering
        */
      inline void
      setFilterFieldName (const std::string &field_name)
      {
        filter_field_name_ = field_name;
      }
 
      /** \brief Get the name of the field used for filtering. */
      inline std::string const
      getFilterFieldName () const
      {
        return (filter_field_name_);
      }
 
      /** \brief Set the field filter limits. All points having field values outside this interval will be discarded.
        * \param[in] limit_min the minimum allowed field value
        * \param[in] limit_max the maximum allowed field value
        */
      inline void
      setFilterLimits (const double &limit_min, const double &limit_max)
      {
        filter_limit_min_ = limit_min;
        filter_limit_max_ = limit_max;
      }
 
      /** \brief Get the field filter limits (min/max) set by the user.
                 The default values are std::numeric_limits<float>::lowest(), std::numeric_limits<float>::max().
        * \param[out] limit_min the minimum allowed field value
        * \param[out] limit_max the maximum allowed field value
        */
      inline void
      getFilterLimits (double &limit_min, double &limit_max) const
      {
        limit_min = filter_limit_min_;
        limit_max = filter_limit_max_;
      }
 
      /** \brief Set to true if we want to return the data outside the interval specified by setFilterLimits (min, max).
        * Default: false.
        * \param[in] limit_negative return data inside the interval (false) or outside (true)
        */
      inline void
      setFilterLimitsNegative (const bool limit_negative)
      {
        filter_limit_negative_ = limit_negative;
      }
 
      /** \brief Get whether the data outside the interval (min/max) is to be returned (true) or inside (false).
        * \param[out] limit_negative true if data \b outside the interval [min; max] is to be returned, false otherwise
        */
      PCL_DEPRECATED(1, 16, "use bool getFilterLimitsNegative() instead")
      inline void
      getFilterLimitsNegative (bool &limit_negative) const
      {
        limit_negative = filter_limit_negative_;
      }
 
      /** \brief Get whether the data outside the interval (min/max) is to be returned (true) or inside (false).
        * \return true if data \b outside the interval [min; max] is to be returned, false otherwise
        */
      inline bool
      getFilterLimitsNegative () const
      {
        return (filter_limit_negative_);
      }
 
    protected:
      /** \brief The size of a leaf. */
      Eigen::Vector4f leaf_size_;
 
      /** \brief Internal leaf sizes stored as 1/leaf_size_ for efficiency reasons. */
      Eigen::Array4f inverse_leaf_size_;
 
      /** \brief Set to true if all fields need to be downsampled, or false if just XYZ. */
      bool downsample_all_data_{true};
 
      /** \brief Set to true if leaf layout information needs to be saved in \a leaf_layout_. */
      bool save_leaf_layout_{false};
 
      /** \brief The leaf layout information for fast access to cells relative to current position **/
      std::vector<int> leaf_layout_;
 
      /** \brief The minimum and maximum bin coordinates, the number of divisions, and the division multiplier. */
      Eigen::Vector4i min_b_, max_b_, div_b_, divb_mul_;
 
      /** \brief The desired user filter field name. */
      std::string filter_field_name_;
 
      /** \brief The minimum allowed filter value a point will be considered from. */
      double filter_limit_min_{std::numeric_limits<float>::lowest()};
 
      /** \brief The maximum allowed filter value a point will be considered from. */
      double filter_limit_max_{std::numeric_limits<float>::max()};
 
      /** \brief Set to true if we want to return the data outside (\a filter_limit_min_;\a filter_limit_max_). Default: false. */
      bool filter_limit_negative_{false};
 
      /** \brief Minimum number of points per voxel for the centroid to be computed */
      unsigned int min_points_per_voxel_{0};
 
      using FieldList = typename pcl::traits::fieldList<PointT>::type;
 
      /** \brief Downsample a Point Cloud using a voxelized grid approach
        * \param[out] output the resultant point cloud message
        */
      void
      applyFilter (PointCloud &output) override;
  };
 
  /** \brief VoxelGrid assembles a local 3D grid over a given PointCloud, and downsamples + filters the data.
    *
    * The VoxelGrid class creates a *3D voxel grid* (think about a voxel
    * grid as a set of tiny 3D boxes in space) over the input point cloud data.
    * Then, in each *voxel* (i.e., 3D box), all the points present will be
    * approximated (i.e., *downsampled*) with their centroid. This approach is
    * a bit slower than approximating them with the center of the voxel, but it
    * represents the underlying surface more accurately.
    *
    * \author Radu B. Rusu, Bastian Steder, Radoslaw Cybulski
    * \ingroup filters
    */
  template <>
  class PCL_EXPORTS VoxelGrid<pcl::PCLPointCloud2> : public Filter<pcl::PCLPointCloud2>
  {
    using Filter<pcl::PCLPointCloud2>::filter_name_;
    using Filter<pcl::PCLPointCloud2>::getClassName;
 
    using PCLPointCloud2 = pcl::PCLPointCloud2;
    using PCLPointCloud2Ptr = PCLPointCloud2::Ptr;
    using PCLPointCloud2ConstPtr = PCLPointCloud2::ConstPtr;
 
    public:
      /** \brief Empty constructor. */
      VoxelGrid () :
        leaf_size_ (Eigen::Vector4f::Zero ()),
        inverse_leaf_size_ (Eigen::Array4f::Zero ()),
 
        min_b_ (Eigen::Vector4i::Zero ()),
        max_b_ (Eigen::Vector4i::Zero ()),
        div_b_ (Eigen::Vector4i::Zero ()),
        divb_mul_ (Eigen::Vector4i::Zero ())
      {
        filter_name_ = "VoxelGrid";
      }
 
      /** \brief Destructor. */
      ~VoxelGrid () override = default;
 
      /** \brief Set the voxel grid leaf size.
        * \param[in] leaf_size the voxel grid leaf size
        */
      inline void
      setLeafSize (const Eigen::Vector4f &leaf_size)
      {
        leaf_size_ = leaf_size;
        // Avoid division errors
        if (leaf_size_[3] == 0)
          leaf_size_[3] = 1;
        // Use multiplications instead of divisions
        inverse_leaf_size_ = Eigen::Array4f::Ones () / leaf_size_.array ();
      }
 
      /** \brief Set the voxel grid leaf size.
        * \param[in] lx the leaf size for X
        * \param[in] ly the leaf size for Y
        * \param[in] lz the leaf size for Z
        */
      inline void
      setLeafSize (float lx, float ly, float lz)
      {
        leaf_size_[0] = lx; leaf_size_[1] = ly; leaf_size_[2] = lz;
        // Avoid division errors
        if (leaf_size_[3] == 0)
          leaf_size_[3] = 1;
        // Use multiplications instead of divisions
        inverse_leaf_size_ = Eigen::Array4f::Ones () / leaf_size_.array ();
      }
 
      /** \brief Get the voxel grid leaf size. */
      inline Eigen::Vector3f
      getLeafSize () const { return (leaf_size_.head<3> ()); }
 
      /** \brief Set to true if all fields need to be downsampled, or false if just XYZ.
        * \param[in] downsample the new value (true/false)
        */
      inline void
      setDownsampleAllData (bool downsample) { downsample_all_data_ = downsample; }
 
      /** \brief Get the state of the internal downsampling parameter (true if
        * all fields need to be downsampled, false if just XYZ).
        */
      inline bool
      getDownsampleAllData () const { return (downsample_all_data_); }
 
      /** \brief Set the minimum number of points required for a voxel to be used.
        * \param[in] min_points_per_voxel the minimum number of points for required for a voxel to be used
        */
      inline void
      setMinimumPointsNumberPerVoxel (unsigned int min_points_per_voxel) { min_points_per_voxel_ = min_points_per_voxel; }
 
      /** \brief Return the minimum number of points required for a voxel to be used.
        */
      inline unsigned int
      getMinimumPointsNumberPerVoxel () const { return min_points_per_voxel_; }
 
      /** \brief Set to true if leaf layout information needs to be saved for later access.
        * \param[in] save_leaf_layout the new value (true/false)
        */
      inline void
      setSaveLeafLayout (bool save_leaf_layout) { save_leaf_layout_ = save_leaf_layout; }
 
      /** \brief Returns true if leaf layout information will to be saved for later access. */
      inline bool
      getSaveLeafLayout () const { return (save_leaf_layout_); }
 
      /** \brief Get the minimum coordinates of the bounding box (after
        * filtering is performed).
        */
      inline Eigen::Vector3i
      getMinBoxCoordinates () const { return (min_b_.head<3> ()); }
 
      /** \brief Get the minimum coordinates of the bounding box (after
        * filtering is performed).
        */
      inline Eigen::Vector3i
      getMaxBoxCoordinates () const { return (max_b_.head<3> ()); }
 
      /** \brief Get the number of divisions along all 3 axes (after filtering
        * is performed).
        */
      inline Eigen::Vector3i
      getNrDivisions () const { return (div_b_.head<3> ()); }
 
      /** \brief Get the multipliers to be applied to the grid coordinates in
        * order to find the centroid index (after filtering is performed).
        */
      inline Eigen::Vector3i
      getDivisionMultiplier () const { return (divb_mul_.head<3> ()); }
 
      /** \brief Returns the index in the resulting downsampled cloud of the specified point.
        * \note for efficiency, user must make sure that the saving of the leaf layout is enabled and filtering performed,
        * and that the point is inside the grid, to avoid invalid access (or use getGridCoordinates+getCentroidIndexAt)
        * \param[in] x the X point coordinate to get the index at
        * \param[in] y the Y point coordinate to get the index at
        * \param[in] z the Z point coordinate to get the index at
        */
      inline int
      getCentroidIndex (float x, float y, float z) const
      {
        return (leaf_layout_.at ((Eigen::Vector4i (static_cast<int> (std::floor (x * inverse_leaf_size_[0])),
                                                   static_cast<int> (std::floor (y * inverse_leaf_size_[1])),
                                                   static_cast<int> (std::floor (z * inverse_leaf_size_[2])),
                                                   0)
                - min_b_).dot (divb_mul_)));
      }
 
      /** \brief Returns the indices in the resulting downsampled cloud of the points at the specified grid coordinates,
        * relative to the grid coordinates of the specified point (or -1 if the cell was empty/out of bounds).
        * \param[in] x the X coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[in] y the Y coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[in] z the Z coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[out] relative_coordinates matrix with the columns being the coordinates of the requested cells, relative to the reference point's cell
        * \note for efficiency, user must make sure that the saving of the leaf layout is enabled and filtering performed
        */
      inline std::vector<int>
      getNeighborCentroidIndices (float x, float y, float z, const Eigen::MatrixXi &relative_coordinates) const
      {
        Eigen::Vector4i ijk (static_cast<int> (std::floor (x * inverse_leaf_size_[0])),
                             static_cast<int> (std::floor (y * inverse_leaf_size_[1])),
                             static_cast<int> (std::floor (z * inverse_leaf_size_[2])), 0);
        Eigen::Array4i diff2min = min_b_ - ijk;
        Eigen::Array4i diff2max = max_b_ - ijk;
        std::vector<int> neighbors (relative_coordinates.cols());
        for (Eigen::Index ni = 0; ni < relative_coordinates.cols (); ni++)
        {
          Eigen::Vector4i displacement = (Eigen::Vector4i() << relative_coordinates.col(ni), 0).finished();
          // checking if the specified cell is in the grid
          if ((diff2min <= displacement.array()).all() && (diff2max >= displacement.array()).all())
            neighbors[ni] = leaf_layout_[((ijk + displacement - min_b_).dot (divb_mul_))]; // .at() can be omitted
          else
            neighbors[ni] = -1; // cell is out of bounds, consider it empty
        }
        return (neighbors);
      }
 
      /** \brief Returns the indices in the resulting downsampled cloud of the points at the specified grid coordinates,
        * relative to the grid coordinates of the specified point (or -1 if the cell was empty/out of bounds).
        * \param[in] x the X coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[in] y the Y coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[in] z the Z coordinate of the reference point (corresponding cell is allowed to be empty/out of bounds)
        * \param[out] relative_coordinates vector with the elements being the coordinates of the requested cells, relative to the reference point's cell
        * \note for efficiency, user must make sure that the saving of the leaf layout is enabled and filtering performed
        */
      inline std::vector<int>
      getNeighborCentroidIndices (float x, float y, float z, const std::vector<Eigen::Vector3i, Eigen::aligned_allocator<Eigen::Vector3i> > &relative_coordinates) const
      {
        Eigen::Vector4i ijk (static_cast<int> (std::floor (x * inverse_leaf_size_[0])), static_cast<int> (std::floor (y * inverse_leaf_size_[1])), static_cast<int> (std::floor (z * inverse_leaf_size_[2])), 0);
        std::vector<int> neighbors;
        neighbors.reserve (relative_coordinates.size ());
        for (const auto &relative_coordinate : relative_coordinates)
          neighbors.push_back (leaf_layout_[(ijk + (Eigen::Vector4i() << relative_coordinate, 0).finished() - min_b_).dot (divb_mul_)]);
        return (neighbors);
      }
 
      /** \brief Returns the layout of the leafs for fast access to cells relative to current position.
        * \note position at (i-min_x) + (j-min_y)*div_x + (k-min_z)*div_x*div_y holds the index of the element at coordinates (i,j,k) in the grid (-1 if empty)
        */
      inline std::vector<int>
      getLeafLayout () const { return (leaf_layout_); }
 
      /** \brief Returns the corresponding (i,j,k) coordinates in the grid of point (x,y,z).
        * \param[in] x the X point coordinate to get the (i, j, k) index at
        * \param[in] y the Y point coordinate to get the (i, j, k) index at
        * \param[in] z the Z point coordinate to get the (i, j, k) index at
        */
      inline Eigen::Vector3i
      getGridCoordinates (float x, float y, float z) const
      {
        return {static_cast<int> (std::floor (x * inverse_leaf_size_[0])),
                                 static_cast<int> (std::floor (y * inverse_leaf_size_[1])),
                                 static_cast<int> (std::floor (z * inverse_leaf_size_[2]))};
      }
 
      /** \brief Returns the index in the downsampled cloud corresponding to a given set of coordinates.
        * \param[in] ijk the coordinates (i,j,k) in the grid (-1 if empty)
        */
      inline int
      getCentroidIndexAt (const Eigen::Vector3i &ijk) const
      {
        int idx = ((Eigen::Vector4i() << ijk, 0).finished() - min_b_).dot (divb_mul_);
        if (idx < 0 || idx >= static_cast<int> (leaf_layout_.size ())) // this checks also if leaf_layout_.size () == 0 i.e. everything was computed as needed
        {
          //if (verbose)
          //  PCL_ERROR ("[pcl::%s::getCentroidIndexAt] Specified coordinate is outside grid bounds, or leaf layout is not saved, make sure to call setSaveLeafLayout(true) and filter(output) first!\n", getClassName ().c_str ());
          return (-1);
        }
        return (leaf_layout_[idx]);
      }
 
      /** \brief Provide the name of the field to be used for filtering data. In conjunction with  \a setFilterLimits,
        * points having values outside this interval will be discarded.
        * \param[in] field_name the name of the field that contains values used for filtering
        */
      inline void
      setFilterFieldName (const std::string &field_name)
      {
        filter_field_name_ = field_name;
      }
 
      /** \brief Get the name of the field used for filtering. */
      inline std::string const
      getFilterFieldName () const
      {
        return (filter_field_name_);
      }
 
      /** \brief Set the field filter limits. All points having field values outside this interval will be discarded.
        * \param[in] limit_min the minimum allowed field value
        * \param[in] limit_max the maximum allowed field value
        */
      inline void
      setFilterLimits (const double &limit_min, const double &limit_max)
      {
        filter_limit_min_ = limit_min;
        filter_limit_max_ = limit_max;
      }
 
      /** \brief Get the field filter limits (min/max) set by the user.
        *        The default values are std::numeric_limits<float>::lowest(), std::numeric_limits<float>::max().
        * \param[out] limit_min the minimum allowed field value
        * \param[out] limit_max the maximum allowed field value
        */
      inline void
      getFilterLimits (double &limit_min, double &limit_max) const
      {
        limit_min = filter_limit_min_;
        limit_max = filter_limit_max_;
      }
 
      /** \brief Set to true if we want to return the data outside the interval specified by setFilterLimits (min, max).
        * Default: false.
        * \param[in] limit_negative return data inside the interval (false) or outside (true)
        */
      inline void
      setFilterLimitsNegative (const bool limit_negative)
      {
        filter_limit_negative_ = limit_negative;
      }
 
      /** \brief Get whether the data outside the interval (min/max) is to be returned (true) or inside (false).
        * \param[out] limit_negative true if data \b outside the interval [min; max] is to be returned, false otherwise
        */
      PCL_DEPRECATED(1, 16, "use bool getFilterLimitsNegative() instead")
      inline void
      getFilterLimitsNegative (bool &limit_negative) const
      {
        limit_negative = filter_limit_negative_;
      }
 
      /** \brief Get whether the data outside the interval (min/max) is to be returned (true) or inside (false).
        * \return true if data \b outside the interval [min; max] is to be returned, false otherwise
        */
      inline bool
      getFilterLimitsNegative () const
      {
        return (filter_limit_negative_);
      }
 
    protected:
      /** \brief The size of a leaf. */
      Eigen::Vector4f leaf_size_;
 
      /** \brief Internal leaf sizes stored as 1/leaf_size_ for efficiency reasons. */
      Eigen::Array4f inverse_leaf_size_;
 
      /** \brief Set to true if all fields need to be downsampled, or false if just XYZ. */
      bool downsample_all_data_{true};
 
      /** \brief Set to true if leaf layout information needs to be saved in \a
        * leaf_layout.
        */
      bool save_leaf_layout_{false};
 
      /** \brief The leaf layout information for fast access to cells relative
        * to current position
        */
      std::vector<int> leaf_layout_;
 
      /** \brief The minimum and maximum bin coordinates, the number of
        * divisions, and the division multiplier.
        */
      Eigen::Vector4i min_b_, max_b_, div_b_, divb_mul_;
 
      /** \brief The desired user filter field name. */
      std::string filter_field_name_;
 
      /** \brief The minimum allowed filter value a point will be considered from. */
      double filter_limit_min_{std::numeric_limits<float>::lowest()};
 
      /** \brief The maximum allowed filter value a point will be considered from. */
      double filter_limit_max_{std::numeric_limits<float>::max()};
 
      /** \brief Set to true if we want to return the data outside (\a filter_limit_min_;\a filter_limit_max_). Default: false. */
      bool filter_limit_negative_{false};
 
      /** \brief Minimum number of points per voxel for the centroid to be computed */
      unsigned int min_points_per_voxel_{0};
 
      /** \brief Downsample a Point Cloud using a voxelized grid approach
        * \param[out] output the resultant point cloud
        */
      void
      applyFilter (PCLPointCloud2 &output) override;
  };
 
  namespace internal
  {
    /** \brief Used internally in voxel grid classes.
      */
    struct cloud_point_index_idx
    {
      unsigned int idx;
      unsigned int cloud_point_index;
 
      cloud_point_index_idx() = default;
      cloud_point_index_idx (unsigned int idx_, unsigned int cloud_point_index_) : idx (idx_), cloud_point_index (cloud_point_index_) {}
      bool operator < (const cloud_point_index_idx &p) const { return (idx < p.idx); }
    };
  }
}
 
#ifdef PCL_NO_PRECOMPILE
#include <pcl/filters/impl/voxel_grid.hpp>
#endif