Can GaussianVoxelMap be used with PCL points?

[themightyoarfish]

Describe the bug
small_gicp-src/include/small_gicp/pcl/pcl_point_traits.hpp refers to .getCovariance4fMap() in set_cov(), but this function does not exist. Hence attempting to use GaussianVoxelMap with pcl point cloud fails.

In file included from /Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/build/_deps/small_gicp-src/include/small_gicp/pcl/pcl_registration.hpp:116:
In file included from /Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/build/_deps/small_gicp-src/include/small_gicp/pcl/pcl_registration_impl.hpp:13:
/Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/build/_deps/small_gicp-src/include/small_gicp/pcl/pcl_point_traits.hpp:33:84: error: no member named 'getCovariance4fMap' in 'pcl::PointXYZI'
   33 |   static Eigen::Matrix4d cov(const Points& points, size_t i) { return points.at(i).getCovariance4fMap().template cast<double>(); }
      |                                                                       ~~~~~~~~~~~~ ^
/Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/build/_deps/small_gicp-src/include/small_gicp/points/traits.hpp:53:21: note: in instantiation of member function 'small_gicp::traits::Traits<pcl::PointCloud<pcl::PointXYZI>>::cov' requested here
   53 |   return Traits<T>::cov(points, i);
      |                     ^
/Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/build/_deps/small_gicp-src/include/small_gicp/ann/incremental_voxelmap.hpp:71:13: note: in instantiation of function template specialization 'small_gicp::GaussianVoxel::add<pcl::PointCloud<pcl::PointXYZI>>' requested here
   71 |       voxel.add(voxel_setting, pt, points, i, T);
      |             ^
/Users/rasmus/Documents/Projects/autocrane-core/tools/lidar/icp_experiments/main.cpp:68:17: note: in instantiation of function template specialization 'small_gicp::IncrementalVoxelMap<small_gicp::GaussianVoxel>::insert<pcl::PointCloud<pcl::PointXYZI>>' requested here
   68 |       voxelmap->insert(*points);

To Reproduce
Steps to reproduce the behavior:

1. install small_gicp
2. Make main function with such content and compile

      auto voxelmap = std::make_shared<small_gicp::GaussianVoxelMap>(0.1);
      voxelmap->insert(pcl::PointCloud<pcl::PointXYZ>());

Expected behavior
Compile error telling me that voxelmap is unsuited with pcl pointclouds, or successful compile.

Environment (please complete the following information):

• OS: macOS
• Version 15.5
• Language C++

[themightyoarfish]

Solution: include include/small_gicp/pcl/pcl_point.hpp and load your pointcloud as pcl::PointCovariance

[themightyoarfish]

However, one needs to register the point struct with POINT_CLOUD_REGISTER_POINT_STRUCT, but its unclear how this can be done. This here does not work

POINT_CLOUD_REGISTER_POINT_STRUCT(pcl::PointCovariance,
                                  (float, x, x)
                                  (float, y, y)
                                  (float, z, z)
                                  (Eigen::Matrix4f, cov, cov))

due to No member named 'value' in 'pcl::traits::asEnum<Eigen::Matrix<float, 4, 4>>'.

[themightyoarfish]

This error occurs when trying to load a PCD file as PointCovariance, i guess you have to get the data without loading it directly from disk?