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NDT-based Lidar Localization

modules/localization/ndt/README.md

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NDT-based Lidar Localization

Introduction

NDT-based lidar localization provide a straightforward, flexible method which combile inspva information and lidar pointcloud to achieve high localization accuracy.

Currently this localization method only works for x86_64 platform

Input

  • Point cloud data from LiDAR sensor ( /apollo/sensor/velodyne64/compensator/PointCloud2)
  • Inspva message from integrated navigation sensor ( /apollo/sensor/gnss/odometry)
  • Localization map (FLAGS_map_dir + "/" + FLAGS_ndt_map_dir + "/" + FLAGS_local_map_name)
  • Parameter config files (velodyne64_novatel_extrinsics_example.yaml, velodyne64_height.yaml, located in modules/localization/msf/params/)

Output

  • Localization result defined by Protobuf message LocalizationEstimate, which can be found in file localization/proto/localization.proto. ( /apollo/localization/pose)

NDT Localization Setting

under some circumstance, we need to balance the speed and accuracy of the algorithm. So we expose some parameters of NDT matching process, It includes online_resolution for online pointcloud, ndt_max_iterations for iterative optimization of NDT matching, ndt_target_resolution for target resolution, ndt_line_search_step_size for searching step size of iteration and ndt_transformation_epsilon for convergence condition.

Generate NDT Localization Map

NDT Localization map is used for NDT-based localization, which is a voxel-grid representation of the environment. Each cell stores the centroid and relative covariance of the points in the cell. The map is organized as a group of map nodes. For more information, please refer to apollo/modules/localization/msf/local_map/ndt_map.

We provide a script (apollo/scripts/ndt_local_map_creator.sh) to generate NDT localization map. You need to provide a group of point cloud frames (as .pcd file), corresponding poses file, and UTM zone id. The format of the poses file is pcd_number timestamp x y z qx qy qz qw.

Visualization Tool

NDT localization also use the same online visualization tool as msf, which can show localization map, point cloud, horizontal position of localization results. This tool is simply launched by ./scripts/localization_online_visualizer.sh.