pcl::VoxelGrid How to get number of points in each voxel grid? - c++

Question

I understand that pcl::VoxelGrid<PointT> can be used to downsample a PointCloud. In my use case, I want to get the number of points within each voxel grid. From PCL docs I found the leaf struct allows me to get the number of points in one voxel by calling getPointCount(). And pcl::VoxelGridCovariance allows me to get a leaf by calling getLeaf(). But I don't know how to apply all of these to a point cloud. I tried to initialize a pcl::VoxelGridCovariance<PointT> by pcl::VoxelGridCovariance<pcl::PCLPointCloud2> grid; but got the error as below. Could anyone know what's the problem here? Or is there any other way to get the number of points in each voxel? Any advice is appreciated!
/usr/local/include/pcl-1.11/pcl/point_struct_traits.h: In instantiation of ‘struct pcl::traits::fieldList<pcl::PCLPointCloud2>’:
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:79:70: required from ‘class pcl::VoxelGridCovariance<pcl::PCLPointCloud2>’
/home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:549:60: required from here
/usr/local/include/pcl-1.11/pcl/point_struct_traits.h:198:8: error: invalid use of incomplete type ‘struct pcl::traits::fieldList<pcl::PCLPointCloud2>’
struct fieldList /** \cond NO_WARN_RECURSIVE */ : fieldList<typename POD<PointT>::type> /** \endcond */
^~~~~~~~~
/usr/local/include/pcl-1.11/pcl/point_struct_traits.h:198:8: note: declaration of ‘struct pcl::traits::fieldList<pcl::PCLPointCloud2>’
In file included from /usr/local/include/pcl-1.11/pcl/point_struct_traits.h:42:0,
from /usr/local/include/pcl-1.11/pcl/type_traits.h:40,
from /usr/local/include/pcl-1.11/pcl/memory.h:46,
from /usr/local/include/pcl-1.11/pcl/io/pcd_io.h:42,
from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:8:
/usr/local/include/pcl-1.11/pcl/point_struct_traits.h:204:3: error: no matching function for call to ‘assertion_failed<false>(mpl_::failed************ (pcl::traits::fieldList<pcl::PCLPointCloud2>::POINT_TYPE_NOT_PROPERLY_REGISTERED::************)(pcl::PCLPointCloud2&))’
BOOST_MPL_ASSERT_MSG((!std::is_same<PointT, typename POD<PointT>::type>::value),
^
/usr/include/boost/mpl/assert.hpp:83:5: note: candidate: template<bool C> int mpl_::assertion_failed(typename mpl_::assert<C>::type)
int assertion_failed( typename assert<C>::type );
^~~~~~~~~~~~~~~~
/usr/include/boost/mpl/assert.hpp:83:5: note: template argument deduction/substitution failed:
/usr/local/include/pcl-1.11/pcl/point_struct_traits.h:204:3: note: cannot convert ‘pcl::traits::fieldList<pcl::PCLPointCloud2>::POINT_TYPE_NOT_PROPERLY_REGISTERED205::assert_arg()’ (type ‘mpl_::failed************ (pcl::traits::fieldList<pcl::PCLPointCloud2>::POINT_TYPE_NOT_PROPERLY_REGISTERED::************)(pcl::PCLPointCloud2&)’) to type ‘mpl_::assert<false>::type {aka mpl_::assert<false>}’
BOOST_MPL_ASSERT_MSG((!std::is_same<PointT, typename POD<PointT>::type>::value),
^
In file included from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:40:0:
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h: In instantiation of ‘class pcl::VoxelGridCovariance<pcl::PCLPointCloud2>’:
/home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:549:60: required from here
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:79:70: error: no type named ‘type’ in ‘struct pcl::traits::fieldList<pcl::PCLPointCloud2>’
using FieldList = typename pcl::traits::fieldList<PointT>::type;
^
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:80:61: error: no type named ‘PointCloud’ in ‘class pcl::Filter<pcl::PCLPointCloud2>’
using PointCloud = typename Filter<PointT>::PointCloud;
^
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:56:9: error: ‘std::__cxx11::string pcl::Filter<pcl::PCLPointCloud2>::filter_name_’ is protected within this context
class VoxelGridCovariance : public VoxelGrid<PointT>
^~~~~~~~~~~~~~~~~~~
In file included from /usr/local/include/pcl-1.11/pcl/filters/filter_indices.h:42:0,
from /usr/local/include/pcl-1.11/pcl/filters/extract_indices.h:42,
from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:13:
/usr/local/include/pcl-1.11/pcl/filters/filter.h:240:19: note: declared protected here
std::string filter_name_;
^~~~~~~~~~~~
In file included from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:40:0:
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:56:9: error: ‘const string& pcl::Filter<pcl::PCLPointCloud2>::getClassName() const’ is protected within this context
class VoxelGridCovariance : public VoxelGrid<PointT>
^~~~~~~~~~~~~~~~~~~
In file included from /usr/local/include/pcl-1.11/pcl/filters/filter_indices.h:42:0,
from /usr/local/include/pcl-1.11/pcl/filters/extract_indices.h:42,
from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:13:
/usr/local/include/pcl-1.11/pcl/filters/filter.h:253:7: note: declared protected here
getClassName () const
^~~~~~~~~~~~
In file included from /home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:40:0:
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h: In instantiation of ‘pcl::VoxelGridCovariance<PointT>::VoxelGridCovariance() [with PointT = pcl::PCLPointCloud2]’:
/home/linux/Documents/waymo_onTheGo/cart_boundary.cpp:549:60: required from here
/usr/local/include/pcl-1.11/pcl/filters/voxel_grid_covariance.h:205:18: error: using invalid field ‘pcl::VoxelGridCovariance<PointT>::voxel_centroids_’
kdtree_ ()
^

Answer 1

To just access the number of points, use OctreePointCloudDensity
To also access the points inside each voxel, use OctreePointCloudPointVector