lidarscanmap

Simultaneous localization and mapping using 2-D lidar scans

Since R2022b

Description

A lidarscanmap object performs simultaneous localization and mapping (SLAM) using the 2-D lidar scans. The lidarscanmap object uses a graph-based SLAM algorithm to create a map of an environment from 2-D lidar scans. First, the algorithm builds a pose graph by linking the input scans using their absolute poses. Then, it uses a scan-matching approach to detect loop closures to minimize any odometry drift.

Using the lidarscanmap object, you can:

• Store and add lidar scans incrementally.

• Detect, add, and delete loop closures.

• Find and update the absolute poses of the scans.

• Generate and visualize a pose graph.

To further optimize the pose graph, use the optimizePoseGraph (Navigation Toolbox) function.

Creation

Syntax

scanMapObj = lidarscanmap

scanMapObj = lidarscanmap(gridResolution)

scanMapObj = lidarscanmap(gridResolution,maxLidarRange)

Description

scanMapObj = lidarscanmap creates a lidarscanmap object with default property values.

scanMapObj = lidarscanmap(gridResolution) specifies the resolution of the occupancy grid map. gridResolution sets the GridResolution property.

scanMapObj = lidarscanmap(gridResolution,maxLidarRange) specifies the resolution of the occupancy grid map and maximum range of the lidar sensor. The gridResolution and maxLidarRange arguments set the GridResolution and the MaxLidarRange properties, respectively.

Properties

ScanAttributes — 2-D lidar scans and absolute poses

table

2-D lidar scans and their absolute poses, stored as a table, where each row represents a lidar scan. The table has these columns.

• ScanID — Unique identifier for the scan, stored as a positive integer.

• LidarScan — 2-D lidar scan, stored as a lidarScan object.

• AbsolutePose — Absolute pose of the lidar scan, stored as a three-element vector of the form [x y Θ], where x and y define the position in meters, and Θ defines the orientation of the input scan in radians.

This property is read-only.

ConnectionAttributes — Connections between lidar scans

table

Connections between lidar scans, stored as a table, where each row represents a connection. The table has these columns.

• FromScanID — ScanID of the scan at the beginning of the connection, stored as a positive integer.

• ToScanID — ScanID of the scan at the end of the connection, stored as a positive integer.

• RelativePose — Relative pose of the corresponding scan specified by ToScanID with respect to the connected scan specified by FromScanID, stored as a three-element vector of the form [x y Θ], where x and y define the translational offset in meters, and Θ defines the rotational offset between the scans in radians.

• InformationMatrix — Uncertainty in the relative pose measurement, stored as a 3-by-3 matrix. This matrix is the inverse of the covariance matrix.

This property is read-only.

LoopClosureIDs — Loop closure between lidar scans

table

Loop closure connections between lidar scans, stored as a table, where each row represents a loop closure. The table has these columns.

• FromScanID — ScanID of the scan at the beginning of the connection, stored as a positive integer.

• ToScanID — ScanID of the scan at the end of the connection, stored as a positive integer.

This property is read-only.

NumScans — Number of lidar scans

positive integer

Number of lidar scans in the lidarscanmap object, specified as a positive integer.

This property is read-only.

Data Types: double

NumConnections — Number of connections

positive integer

Number of connections in the lidarscanmap object, specified as a positive integer.

This property is read-only.

Data Types: double

NumLoopClosures — Number of loop closure connections

positive integer

Number of loop closure connections in the lidarscanmap object, specified as a positive integer.

This property is read-only.

Data Types: double

GridResolution — Resolution of occupancy grid map

positive scalar

Resolution of the occupancy grid map, specified as a positive scalar.

To set this property, you must specify it at object creation.

Data Types: double

MaxLidarRange — Maximum range of lidar sensor

positive scalar

Maximum range of the lidar sensor, specified as a positive scalar. Units are in meters.

To set this property, you must specify it at object creation.

Data Types: double

Object Functions

addScan	Add 2-D lidar scan to map
detectLoopClosure	Detect loop closure in 2-D lidar scan map
addLoopClosure	Add loop closure to the map
deleteLoopClosure	Delete loop closure between 2-D lidar scans
poseGraph	Create 2-D pose graph from lidar scan map
findPose	Find absolute pose of 2-D lidar scan in the map
updateScanPoses	Update absolute poses of 2-D lidar scans
copy	Create a copy of lidarscanmap object
show	Display 2-D lidar scans and lidar sensor trajectory

Examples

Localize 2-D Lidar Scans in Map

Load a MAT file containing 2-D lidar scans and a warehouse map into the workspace.

data = load("wareHouse.mat");
scans = data.wareHouseScans;

Create a lidarscanmap object.

scanMapObj = lidarscanmap;

Add the scans from the input data to the scanMapObj object by using the addScan function.

for currentID = 1:70
    addScan(scanMapObj,scans{currentID});
end

Display the warehouse map.

ax = show(scanMapObj,ShowTrajectory=false);
hold on

Find the absolute pose of the first scan in the map by using the findPose function. Specify the pose estimate of the scan as [0 0] and the search radius as 5 meters.

absPose = findPose(scanMapObj,scans{1},[0 0],SearchRadius=5);

Display the pose of the first scan in the map.

showShape("circle",[absPose(1:2) 0.2],Color="g",Parent=ax)

Iterate the previous two steps to localize the remaining scans in the map and visualize the results.

for n = 2:numel(scans)
    currentScan = scans{n};

    % Use the absolute pose of the previous scan as the pose estimate for
    % the next scan
    poseEstimate = absPose(1:2);
    absPose = findPose(scanMapObj,currentScan,poseEstimate,SearchRadius=5);

    % Display the pose of the current scan in the map
    pose = [absPose(1:2) 0.05];
    showShape("circle",pose,Color="b")
end
hold off

Version History

Introduced in R2022b