Global map is uniform but too sparse vs. local LiDAR scans — how to keep final global map dense (high-point sensor)?

[mahmood-ul-hasan]

Hi! I’m mapping indoors with a high-point LiDAR (Airy; very dense raw scans). During run/visualization the local scans are dense, but the final global map looks uniform yet notably sparser than the local data. I’m aiming for a dense final global map that preserves as much of the original point density as feasible.

What I’m seeing

• Local LiDAR sweep (near real time): dense point clouds (as expected for this sensor).
• Final/global map after submapping + global mapping: Much less dense than the local scans.

Question for the authors: which parameters (and stages) directly control the final global map density? I’d like to confirm which settings actually cap or decimate points written into submaps / the global model (vs. params that only affect registration or internal voxel maps).

My current relevant config (abridged):

"sub_mapping": {
  "submap_downsample_resolution": 0.1,
  "submap_target_num_points": 50000,
  "max_num_keyframes": 15,
  "keyframe_update_strategy": "OVERLAP",
  "keyframe_voxel_resolution": 0.2,
  "keyframe_voxelmap_levels": 3
},
"global_mapping": {
  "submap_voxel_resolution": 0.2,
  "submap_voxel_resolution_max": 0.2,
  "submap_voxel_resolution_dmin": 1000000000.0,
  "submap_voxel_resolution_dmax": 1000000000.0,
  "submap_voxelmap_levels": 1,
  "randomsampling_rate": 1.0,
  "registration_error_factor_type": "VGICP_GPU"
}

Could you please advise on best-practice settings for dense global maps with high-point sensors? Concretely:

1. Which parameters truly limit the number of points stored in each submap and thus visible in the final global map?

   • Is submap_downsample_resolution the main choke point?
   • Does submap_target_num_points hard-cap the stored points per submap (and should I set it to a higher value or -1)?

2. Is there any additional downsampling at the global mapping or export stage that I should disable/tighten?

3. For high-density LiDAR (Airy), what ranges would you recommend as starting points? For example:

   • submap_downsample_resolution: 0.05 / 0.03?
   • submap_target_num_points: 150k / 200k / -1?
   • max_num_keyframes: 40–60?
   • Keep global_mapping.submap_voxel_resolution at 0.2 or push to 0.1?

Thanks a lot — happy to test a recommended configuration.