Mapping using GMapping

Overview

GMapping is a commonly used open source SLAM algorithm based on the filtering SLAM framework. GMapping effectively utilizes the wheel odometry information and does not require high frequency of laser LiDAR. When mapping small environments, little processing power is required is low and the accuracy is high.

You can find more information on the openslam_gmapping and slam_gmapping GitHub repositories.

Structure

Usage

Note

Use Ctrl + C command to end all the processes before running the below commands.

Note

Mapping works best when the LIMO drives slowly through its environment. If it moves around too quickly, mapping quality will be affected.

Mapping

1. Start the LIMO. Open a new terminal, and enter the command:

   $ roslaunch limo_bringup limo_start.launch pub_odom_tf:=false
   

2. Launch the GMapping processes. In a new terminal, and enter the command:

   $ roslaunch limo_bringup limo_gmapping.launch
   

   After launching successfully, RViz will be opened and display something like the image below.

   

3. Use the mobile app to explore and map out the environment.

Saving the Map

When finished mapping, do the following to save the map to the specified directory:

1. Switch to the directory where you need to save the map. For example, if you want to save the map to ~/agilex_ws/src/limo_ros/limo_bringup/maps/, enter the command:

   cd ~/agilex_ws/src/limo_ros/limo_bringup/maps/
   

2. After switching to ~/agilex_ws/limo_bringup/maps, enter the command:

   rosrun map_server map_saver -f map1
   

   This calls the map_saver script from the map_server package to save the map to a file in the current directory, in this case map1 in ~/agilex_ws/limo_bringup/maps.

Note

Use different names for different maps, else you risk overwriting existing map files.

Configuration

The GMapping package can be configured using the launch file at ~/agilex_ws/src/limo_ros/limo_bringup/launch/limo_gmapping.launch

Parameter	Type	Default	Description
~throttle_scans	int	1	The scan data threshold to be processed; the default is to process 1 scan data at a time (it can be set larger to skip some scan data)
~base_frame	string	base_link	Robot base coordinate system
~map_frame	string	map	Map coordinate system
~odom_frame	string	odom	Odometer coordinate system
~map_update_interval	float	5.0	Map update frequency
~maxUrange	float	80	Detect the maximum available range, that is, the range that the beam can reach
~sigma	float	0.05	Standard deviation of endpoint matching
~kernelSize	int	1	Used to find the corresponding kernel size
~lstep	float	0.05	Translation optimization step
~astep	float	0.05	Rotation optimization step
~iterations	int	5	Scan matching iterations
~lsigma	float	0.075	Laser standard deviation for likelihood calculation
~ogain	float	3.0	Used for smooth resampling effect during likelihood calculation
~lskip	int	0	The number of beams skipped in each scan.
~minimumScore	float	0.0	The lowest value of the scan matching result
~srr	float	0.1	The mileage error during translation as a translation function (rho/rho)
~srt	float	0.2	The mileage error during translation as a rotation function (rho/theta)
~str	float	0.1	The mileage error during rotation as a translation function(theta/rho)
~stt	float	0.2	The mileage error during rotation as a rotation function (theta/theta)
~linearUpdate	float	1.0	The robot translates a certain distance and processes the laser data once
~angularUpdate	float	0.5	The robot rotates a certain distance and processes the laser data once
~temporalUpdate	float	-1.0	If the latest scan processing is slower than the update, one scan is processed. Turn off time-based updates when the value is negative.
~resampleThreshold	float	0.5	Resampling threshold based on Neff
~particles	int	30	Number of particles in the filter
~xmin	float	-100.0	The initial minimum size of the map in the x direction
~ymin	float	-100.0	The initial minimum size of the map in the y direction
~xmax	float	100.0	The initial maximum size of the map in the x direction
~ymax	float	100.0	The initial maximum size of the map in the y direction
~delta	float	0.05	Map resolution
~llsamplerange	float	0.01	The translation sampling distance of likelihood calculation
~llsamplestep	float	0.01	The translation sampling step of likelihood calculation
~lasamplerange	float	0.005	The angle sampling distance of likelihood calculation
~lasamplestep	float	0.005	The angle sampling step of likelihood calculation
~transform_publish_period	float	0.05	TF transform publishing period
~occ_thresh	float	0.25	The threshold of raster map occupancy rate
~maxRange	float	——	The maximum range of sensor