cartographer/mapping/proto/submap.proto¶

Overview¶

submap.proto defines the serialized state of a Submap2D and a Submap3D. These messages are embedded in the serialization format (via proto::Submap in serialization.proto) and are produced by Submap2D::ToProto / Submap3D::ToProto and consumed by their corresponding constructors.

Submap2D¶

// Serialized state of a Submap2D.
message Submap2D {
  transform.proto.Rigid3d local_pose = 1;
  int32 num_range_data = 2;
  bool finished = 3;
  Grid2D grid = 4;
}

Field	Type	Meaning
`local_pose`	`transform.proto.Rigid3d`	Pose of the submap in the local (tracking) frame
`num_range_data`	int32	Number of range data scans inserted so far
`finished`	bool	Whether the submap is finished (no more insertions)
`grid`	`Grid2D`	The underlying grid (ProbabilityGrid or TSDF2D)

Grid2D (from grid_2d.proto) carries the grid’s MapLimits, the flat cells array (values are actually int16 stored as int32), the known_cells_box, a oneof choosing probability_grid_2d or tsdf_2d, and the min/max correspondence costs:

message Grid2D {
  message CellBox { int32 max_x = 1; int32 max_y = 2; int32 min_x = 3; int32 min_y = 4; }
  MapLimits limits = 1;
  repeated int32 cells = 2;            // int16 values
  CellBox known_cells_box = 3;
  oneof grid {
    ProbabilityGrid probability_grid_2d = 4;
    TSDF2D tsdf_2d = 5;
  }
  float min_correspondence_cost = 6;
  float max_correspondence_cost = 7;
}

Submap3D¶

// Serialized state of a Submap3D.
message Submap3D {
  transform.proto.Rigid3d local_pose = 1;
  int32 num_range_data = 2;
  bool finished = 3;
  HybridGrid high_resolution_hybrid_grid = 4;
  HybridGrid low_resolution_hybrid_grid = 5;
  repeated float rotational_scan_matcher_histogram = 6;
}

Field	Type	Meaning
`local_pose`	`transform.proto.Rigid3d`	Pose of the submap in the local frame
`num_range_data`	int32	Number of inserted range data scans
`finished`	bool	Submap finished flag
`high_resolution_hybrid_grid`	`HybridGrid`	Dense occupancy voxel grid at high resolution
`low_resolution_hybrid_grid`	`HybridGrid`	Sparse occupancy voxel grid at low resolution
`rotational_scan_matcher_histogram`	repeated float	Histogram used by the rotational scan matcher for 3D loop closure

HybridGrid (from hybrid_grid.proto) stores a sparse voxel grid as parallel arrays:

message HybridGrid {
  float resolution = 1;
  repeated sint32 x_indices = 3;  // '{x,y,z}_indices[i]' is the index of 'values[i]'
  repeated sint32 y_indices = 4;
  repeated sint32 z_indices = 5;
  repeated int32 values = 6;      // uint16 values stored as int32
}

Role in the SLAM Pipeline¶

Serialization — Submap2D/Submap3D are written as part of SerializedData.submap inside the serialization stream.
Deserialization — the submaps’ constructors rebuild the grid(s) from the proto, restoring the local pose, range count, and finished flag so the pose graph can resume optimization.
Submap query / visualization — grid data also feeds the submap query response used by rviz and the map server.

See Also¶

Serialization — Embeds these messages in the map state stream
Submap2D — C++ type serialized here
Submap3D — C++ type serialized here
ProbabilityGrid — Grid payload for 2D submaps
HybridGrid — Grid payload for 3D submaps