lidarScan

Create object for storing 2-D lidar scan

Description

A lidarScan object contains data for a single 2-D lidar (light detection and ranging) scan. The lidar scan is a laser scan for a 2-D plane with distances (Ranges) measured from the sensor to obstacles in the environment at specific angles (Angles). Use this laser scan object as an input to other robotics algorithms such as matchScans, controllerVFH, or monteCarloLocalization.

Creation

Syntax

scan = lidarScan(ranges,angles)

scan = lidarScan(cart)

Description

scan = lidarScan(ranges,angles) creates a lidarScan object from the ranges and angles, that represent the data collected from a lidar sensor. The ranges and angles inputs are vectors of the same length and are set directly to the Ranges and Angles properties.

scan = lidarScan(cart) creates a lidarScan object using the input Cartesian coordinates as an n-by-2 matrix. The Cartesian property is set directly from this input.

scan = lidarScan(scanMsg) creates a lidarScan object from a LaserScan (ROS Toolbox) ROS message object.

Properties

Ranges — Range readings from lidar in meters

vector

Range readings from lidar, specified as a vector in meters. This vector is the same length as Angles, and the vector elements are measured in meters.

Data Types: single | double

Angles — Angle of readings from lidar in radians

vector

Angle of range readings from lidar, specified as a vector. This vector is the same length as Ranges, and the vector elements are measured in radians. Angles are measured counter-clockwise around the positive z-axis.

Data Types: single | double

Cartesian — Cartesian coordinates of lidar readings in meters

[x y] matrix

Cartesian coordinates of lidar readings, returned as an [x y] matrix. In the lidar coordinate frame, positive x is forward and positive y is to the left.

Data Types: single | double

Count — Number of lidar readings

scalar

Number of lidar readings, returned as a scalar. This scalar is also equal to the length of the Ranges and Angles vectors or the number of rows in Cartesian.

Data Types: double

Object Functions

plot	Display laser or lidar scan readings
removeInvalidData	Remove invalid range and angle data
transformScan	Transform laser scan based on relative pose

Examples

Plot Lidar Scan and Remove Invalid Points

Specify lidar data as vectors of ranges and angles. These values include readings outside of the sensors range.

x = linspace(-2,2);
ranges = abs((1.5).*x.^2 + 5);
ranges(45:55) = 3.5;
angles = linspace(-pi/2,pi/2,numel(ranges));

Create a lidar scan by specifying the ranges and angles. Plot all points of the lidar scan.

scan = lidarScan(ranges,angles);
plot(scan)

Remove invalid points based on a specified minimum and maximum range.

minRange = 0.1;
maxRange = 7;
scan2 = removeInvalidData(scan,'RangeLimits',[minRange maxRange]);
hold on
plot(scan2)
legend('All Points','Valid Points')

Transform Laser Scans

Create a lidarScan object. Specify the ranges and angles as vectors.

refRanges = 5*ones(1,300);
refAngles = linspace(-pi/2,pi/2,300);
refScan = lidarScan(refRanges,refAngles);

Translate the laser scan by an [x y] offset of (0.5,0.2).

transformedScan = transformScan(refScan,[0.5 0.2 0]);

Rotate the laser scan by 20 degrees.

rotateScan = transformScan(refScan,[0,0,deg2rad(20)]);

Match Lidar Scans

Create a reference lidar scan using lidarScan (Robotics System Toolbox). Specify ranges and angles as vectors.

refRanges = 5*ones(1,300);
refAngles = linspace(-pi/2,pi/2,300); 
refScan = lidarScan(refRanges,refAngles);

Using the transformScan (Robotics System Toolbox) function, generate a second lidar scan at an x,y offset of (0.5,0.2).

currScan = transformScan(refScan,[0.5 0.2 0]);

Match the reference scan and the second scan to estimate the pose difference between them.

pose = matchScans(currScan,refScan);

Use the transformScan function to align the scans by transforming the second scan into the frame of the first scan using the relative pose difference. Plot both the original scans and the aligned scans.

currScan2 = transformScan(currScan,pose);

subplot(2,1,1);
hold on
plot(currScan)
plot(refScan)
title('Original Scans')
hold off

subplot(2,1,2);
hold on
plot(currScan2)
plot(refScan)
title('Aligned Scans')
xlim([0 5])
hold off

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

Lidar scans require a limited size in code generation. The lidar scans are limited to 40,000 points (range and angles) as a maximum.

Version History

Introduced in R2019b