Merge pull request #5969 from mvieth/ndt_gettargetcells

NDT: allow access to target cloud distribution

registration/include/pcl/registration/ndt.h

@@ -220,6 +220,20 @@ class NormalDistributionsTransform
     return nr_iterations_;
   }
 
+  /** \brief Get access to the `VoxelGridCovariance` generated from target cloud
+   * containing point means and covariances. Set the input target cloud before calling
+   * this. Useful for debugging, e.g.
+   * \code
+   * pcl::PointCloud<PointXYZ> visualize_cloud;
+   * ndt.getTargetCells().getDisplayCloud(visualize_cloud);
+   * \endcode
+   */
+  inline const TargetGrid&
+  getTargetCells() const
+  {
+    return target_cells_;
+  }
+
   /** \brief Convert 6 element transformation vector to affine transformation.
    * \param[in] x transformation vector of the form [x, y, z, roll, pitch, yaw]
    * \param[out] trans affine transform corresponding to given transformation
@@ -292,6 +306,10 @@ class NormalDistributionsTransform
     target_cells_.setInputCloud(target_);
     // Initiate voxel structure.
     target_cells_.filter(true);
+    PCL_DEBUG("[pcl::%s::init] Computed voxel structure, got %zu voxels with valid "
+              "normal distributions.\n",
+              getClassName().c_str(),
+              target_cells_.getCentroids()->size());
   }
 
   /** \brief Compute derivatives of likelihood function w.r.t. the