Added getter for point indices in hull computation

- Added method 'getHullPointIndices ()' in 'pcl::ConvexHull' and
  'pcl::ConcaveHull' to retrieve the indices of the input cloud that
  compose the hull. This might be helpful if the input point cloud is
  organized the hull needs to be retrieved while retaining the
  underlying organization of the point cloud data.
- Point indices are stored via new member of type pcl::PointIndices

surface/include/pcl/surface/concave_hull.h

@@ -157,6 +157,16 @@ namespace pcl
           PCL_ERROR ("[pcl::%s::setDimension] Invalid input dimension specified!\n", getClassName ().c_str ());
       }
 
+      /** \brief Retrieve the indices of the input point cloud that for the convex hull.
+        *
+        * \note Should only be called after reconstruction was performed and if the ConcaveHull is
+        * set to preserve information via setKeepInformation ().
+        *
+        * \param[out] hull_point_indices The indices of the points forming the point cloud
+        */
+      void
+      getHullPointIndices (pcl::PointIndices &hull_point_indices) const;
+
     protected:
       /** \brief Class get name method. */
       std::string
@@ -197,6 +207,9 @@ namespace pcl
 
       /** \brief the dimensionality of the concave hull */
       int dim_;
+
+      /** \brief vector containing the point cloud indices of the convex hull points. */
+      pcl::PointIndices hull_indices_;
   };
 }
 

surface/include/pcl/surface/convex_hull.h

@@ -166,6 +166,14 @@ namespace pcl
         return (dimension_);
       }
 
+      /** \brief Retrieve the indices of the input point cloud that for the convex hull.
+        *
+        * \note Should only be called after reconstruction was performed.
+        * \param[out] hull_point_indices The indices of the points forming the point cloud
+        */
+      void
+      getHullPointIndices (pcl::PointIndices &hull_point_indices) const;
+
     protected:
       /** \brief The actual reconstruction method. 
         * 
@@ -255,6 +263,9 @@ namespace pcl
       /* \brief z-axis - for checking valid projections. */
       const Eigen::Vector3d z_axis_;
 
+      /* \brief vector containing the point cloud indices of the convex hull points. */
+      pcl::PointIndices hull_indices_;
+
       public:
         EIGEN_MAKE_ALIGNED_OPERATOR_NEW
   };

surface/include/pcl/surface/impl/concave_hull.hpp

@@ -579,18 +579,18 @@ pcl::ConcaveHull<PointInT>::performReconstruction (PointCloud &alpha_shape, std:
     distances.resize (1);
 
     // for each point in the concave hull, search for the nearest neighbor in the original point cloud
-
-    std::vector<int> indices;
-    indices.resize (alpha_shape.points.size ());
+    hull_indices_.header = input_->header;
+    hull_indices_.indices.clear ();
+    hull_indices_.indices.reserve (alpha_shape.points.size ());
 
     for (size_t i = 0; i < alpha_shape.points.size (); i++)
     {
       tree.nearestKSearch (alpha_shape.points[i], 1, neighbor, distances);
-      indices[i] = neighbor[0];
+      hull_indices_.indices.push_back (neighbor[0]);
     }
 
     // replace point with the closest neighbor in the original point cloud
-    pcl::copyPointCloud (*input_, indices, alpha_shape);
+    pcl::copyPointCloud (*input_, hull_indices_.indices, alpha_shape);
   }
 }
 #ifdef __GNUC__
@@ -617,6 +617,12 @@ pcl::ConcaveHull<PointInT>::performReconstruction (std::vector<pcl::Vertices> &p
   performReconstruction (hull_points, polygons);
 }
 
+//////////////////////////////////////////////////////////////////////////////////////////
+template <typename PointInT> void
+pcl::ConcaveHull<PointInT>::getHullPointIndices (pcl::PointIndices &hull_point_indices) const
+{
+  hull_point_indices = hull_indices_;
+}
 
 #define PCL_INSTANTIATE_ConcaveHull(T) template class PCL_EXPORTS pcl::ConcaveHull<T>;
 

surface/include/pcl/surface/impl/convex_hull.hpp

@@ -260,8 +260,13 @@ pcl::ConvexHull<PointInT>::performReconstruction2D (PointCloud &hull, std::vecto
   polygons.resize (1);
   polygons[0].vertices.resize (hull.points.size ());
 
+  hull_indices_.header = input_->header;
+  hull_indices_.indices.clear ();
+  hull_indices_.indices.reserve (hull.points.size ());
+
   for (int j = 0; j < static_cast<int> (hull.points.size ()); j++)
   {
+    hull_indices_.indices.push_back ((*indices_)[idx_points[j].first]);
     hull.points[j] = input_->points[(*indices_)[idx_points[j].first]];
     polygons[0].vertices[j] = static_cast<unsigned int> (j);
   }
@@ -357,10 +362,15 @@ pcl::ConvexHull<PointInT>::performReconstruction3D (
   ++max_vertex_id;
   std::vector<int> qhid_to_pcidx (max_vertex_id);
 
+  hull_indices_.header = input_->header;
+  hull_indices_.indices.clear ();
+  hull_indices_.indices.reserve (num_vertices);
+
   FORALLvertices
   {
-    // Add vertices to hull point_cloud
-    hull.points[i] = input_->points[(*indices_)[qh_pointid (vertex->point)]];
+    // Add vertices to hull point_cloud and store index
+    hull_indices_.indices.push_back ((*indices_)[qh_pointid (vertex->point)]);
+    hull.points[i] = input_->points[(*indices_)[hull_indices_.indices.back ()]];
 
     qhid_to_pcidx[vertex->id] = i; // map the vertex id of qhull to the point cloud index
     ++i;
@@ -481,6 +491,12 @@ pcl::ConvexHull<PointInT>::reconstruct (PointCloud &points, std::vector<pcl::Ver
 
   deinitCompute ();
 }
+//////////////////////////////////////////////////////////////////////////
+template <typename PointInT> void
+pcl::ConvexHull<PointInT>::getHullPointIndices (pcl::PointIndices &hull_point_indices) const
+{
+  hull_point_indices = hull_indices_;
+}
 
 #define PCL_INSTANTIATE_ConvexHull(T) template class PCL_EXPORTS pcl::ConvexHull<T>;